What Is Gerrymandering
Gerrymandering is drawing election district lines on purpose so one party wins more seats than its share of the vote, or so a group of voters loses its power to elect anyone. It happens when states redraw districts, usually after each census and now sometimes in the middle of a decade. Both parties do it.
Key facts
- Two techniques do the work: packing one side’s voters into a few districts and cracking the rest across many.
- In 2016, North Carolina Republicans won 10 of 13 House seats with 53% of the statewide vote (Rucho v. Common Cause).
- Since 2019, federal courts cannot hear claims that a map is too partisan, so only state courts, state laws or Congress can stop one.
- Maps used in 2024 had 16 fewer Democratic-leaning districts than fair-standard maps would (Brennan Center).
- 9 states redrew their House maps for 2026, 7 toward Republicans and 2 toward Democrats.
The word dates to 1812. Massachusetts Governor Elbridge Gerry signed a state Senate map with one district shaped so oddly that a drawing of it as a salamander-like monster ran in the Boston Gazette under the headline “The Gerry-mander” (Smithsonian). The practice is older than the name. When Virginia drew its first congressional map, Patrick Henry tried to draw the lines so that James Madison could not win a seat (Brennan Center).
Two centuries later the pen is software. Mapmakers load precinct-level election results and can test thousands of versions of a map before picking the one that holds up best for their side.
How Packing and Cracking Work
Packing crams one side’s voters into as few districts as possible. They win those seats by huge margins, and every vote past a bare majority does them no good. Cracking splits the rest across many districts, where they fall just short of a majority in each one. Mapmakers use both at once.
The same 50 voters can elect a 5-0, 3-2, or 2-3 delegation. Only the lines change.
One state, 30 Blue voters and 20 Red voters, five districts of 10 voters each
In the third map, the party with 40% of the voters wins 60% of the seats. Nobody’s ballot was changed, and every district has the same number of people.
You cannot spot a gerrymander by its shape. After a court struck down a North Carolina district built around North Carolina A&T State University as a racial gerrymander in 2016, lawmakers split the campus between two compact, ordinary-looking districts that Republicans would comfortably win (Brennan Center). Some odd shapes are innocent, because they follow a river, a county line, or a community that wants to stay together.
Real Examples of Gerrymandering
The clearest examples come from court records, where mapmakers had to explain under oath what they did and why.
Five gerrymanders from the public record
Source: Rucho v. Common Cause (2019) for North Carolina and Maryland; Brennan Center for Illinois and Texas; Alexander v. South Carolina NAACP (2024)
North Carolina: A Map Drawn for 10 Republicans
After a federal court struck down two districts as racial gerrymanders in 2016, North Carolina’s Republican leaders told their mapmaker to draw a replacement that kept the 10-3 split. The committee adopted a written criterion called “Partisan Advantage.” Its co-chair, Rep. David Lewis, told legislators the map aimed to elect 10 Republicans and 3 Democrats because he did “not believe it [would be] possible to draw a map with 11 Republicans and 2 Democrats.” He added: “I think electing Republicans is better than electing Democrats” (Rucho v. Common Cause).
Under both of North Carolina’s 2010s maps, Republicans won about three-quarters of the seats with about half the vote.
| Group | Share of votes | Share of seats | Change |
|---|---|---|---|
| 2012 (2011 map): 9 of 13 seats | 49.0% | 69.2% | +20.2 pts |
| 2016 (2016 map): 10 of 13 seats | 53.0% | 76.9% | +23.9 pts |
| 2018 (2016 map): 9 of 12 seats filled | 50.0% | 75.0% | +25.0 pts |
Vote shares as stated in Rucho v. Common Cause (2019), majority and dissent. Seat shares computed from the seat counts. One 2018 seat was left vacant after election fraud.
Some gap between votes and seats is normal when each district elects one winner. A gap this size, held steady while the vote moved from 49% to 53%, is what the map was built to produce. It happened again after 2023: with about 52% of the vote, Republicans won half the seats under a court-drawn map in 2022 and 10 of 14 under the legislature’s new map in 2024 (redistricting explainer).
Maryland: Democrats Did It Too
Maryland’s Democratic governor, Martin O’Malley, later said that he set out “to create a map that was more favorable for Democrats over the next ten years,” and that “a decision was made to go for the Sixth,” a Republican-held district. New census figures required moving only about 10,000 people out of it. The map moved about 360,000 out and 350,000 in. Democrats then won 7 of Maryland’s 8 seats in each election from 2012 through 2018, never with more than 65% of the vote (Rucho v. Common Cause, Kagan dissent).
Types of Gerrymandering
Partisan Gerrymandering
Partisan gerrymandering draws lines so one party wins more seats than its share of the vote. Republicans controlled the map in far more states after the 2020 census, which is why the national tilt favors them. Democrats gerrymander where they hold the pen, as Illinois and Maryland show (Brennan Center).
Racial Gerrymandering
Racial gerrymandering sorts voters mainly by race, packing or cracking communities of color so they elect fewer candidates of their choice. It is unconstitutional. In the South, though, race and party often line up, so a state can defend a map that moved Black voters by saying it was moving Democrats. That is the argument the Supreme Court accepted from South Carolina in 2024. The Voting Rights Act has been the main tool against these maps.
Malapportionment
Malapportionment is the oldest form: districts with very different populations, so a voter in a small district counts for more than a voter in a large one. Before the 1960s, some state legislative districts held many times the population of others. The Supreme Court ended that with the “one person, one vote” rulings, Wesberry v. Sanders (1964) for congressional districts and Reynolds v. Sims (1964) for state legislatures. “Legislators represent people, not trees or acres,” Chief Justice Earl Warren wrote in Reynolds (Reynolds v. Sims). That is why every modern gerrymander uses districts of equal population and moves voters instead.
Prison Gerrymandering
The Census counts incarcerated people at the prison, not at home. A district with a large prison gains population, and so political weight, from people who cannot vote there, while their home neighborhoods lose it. Nineteen states have ended some part of the practice, and fewer apply the fix to congressional maps (Prison Gerrymandering Project, January 2026). Our census explainer covers who else the count misses.
Is Gerrymandering Legal?
Partisan gerrymandering is effectively legal under federal law. Racial gerrymandering is not, but it has become much harder to prove. State constitutions are where most of the remaining limits live.
Three Supreme Court decisions in seven years set that line.
- Federal courts step back
- Party can explain race
- Voting Rights Act claims narrowed
: 2019: Federal courts step back (Rucho: partisan gerrymandering claims are a political question). 2024: Party can explain race (Alexander: challengers must rule out politics as the reason). 2026: Voting Rights Act claims narrowed (Callais: new proof burdens for a challenge to a map).
2019, Rucho v. Common Cause (5-4). Chief Justice John Roberts, quoting an earlier ruling, wrote that such gerrymandering is “incompatible with democratic principles,” but that federal courts have no standard to judge it. Partisan gerrymandering claims are now for state courts, state legislatures, and Congress. Justice Elena Kagan wrote in dissent that “these gerrymanders enabled politicians to entrench themselves in office as against voters’ preferences” (Rucho opinion).
2024, Alexander v. South Carolina NAACP (6-3). South Carolina moved a large part of Charleston County out of the 1st District. The trial court found that more than 60% of the Black Charleston County residents in the 1st District were moved to the 6th, and that 10 of the 11 precincts with the most Black residents left the district. The state said its goal was a safer Republican seat. The Court held that challengers had not shown race, rather than party, drove the lines (Alexander opinion).
2026, Louisiana v. Callais (6-3). The Court ruled that Louisiana’s second Black-majority district was an unconstitutional racial gerrymander and changed what a Voting Rights Act challenge must prove. Challengers now have to show that voting patterns are not explained by party and offer sample maps that meet the state’s political goals. The redistricting explainer sets out the before and after.
Where a challenge to a gerrymandered map can go now
How Researchers Measure a Partisan Map
The best-known yardstick is the efficiency gap. It counts each party’s “wasted” votes (votes for a losing candidate, plus a winner’s votes beyond what was needed) and compares the totals. Its creators, Nicholas Stephanopoulos and Eric McGhee, found that a gap of about 7% has historically been enough to lock in a majority until the next redistricting. In 2012, 15 of the 38 state legislative maps they measured were over that line, and Wisconsin’s Assembly map scored about 13% (University of Chicago Law School). The Supreme Court never adopted it before Rucho closed the door.
State Courts Still Act
State courts, including those in Alaska, Ohio, Utah, and Wisconsin, have struck down maps under their state constitutions. Enforcement is uneven. Ohio’s mapmakers kept using maps the state supreme court had rejected, and North Carolina’s supreme court reversed its own anti-gerrymandering ruling in 2023 after its membership changed (State Court Report; Brennan Center). The next year, North Carolina’s new map flipped three Democratic seats, enough to decide control of the U.S. House (Brennan Center).
Mid-Decade Gerrymanders for the 2026 Election
Maps used to change once a decade, after the census. Before 2025, only two states had redrawn their congressional maps mid-decade by choice since 1970 (Ballotpedia). For the 2026 election, nine states have new maps, adopted by legislatures, a commission, voters and courts.
The new maps in effect for 2026 were drawn to shift 15 seats toward Republicans and 6 toward Democrats, a net of 9 toward Republicans. Those are the seats the maps were designed to move, not a forecast of who will win.
Congressional maps redrawn for the 2026 election
Source: Ballotpedia and state reporting, verified October 14, 2026
Other attempts failed or stalled. Missouri passed a map in 2025 and used it in the August primary, but voters petitioned for a referendum on it. On September 3, 2026, the Missouri Supreme Court kept the 2022 map for this year’s general election and left the new map to voters as Proposition A on the November 3 ballot (PBS News). Federal courts then ordered the new map used, and on September 25 the U.S. Supreme Court stayed those orders, so the 2022 map stands for November (Supreme Court order). Virginia voters approved an amendment allowing a new map, and the state supreme court struck it down on May 8, 2026. Indiana’s Republican Senate refused to redraw. To see whether your own state changed its map and who drew it, use the state finder on the redistricting page.
The Callais ruling sped up the Southern redraws. Within weeks, Tennessee split Memphis across three Republican districts, ending the state’s only majority-Black seat, and Louisiana dismantled its second Black-majority district.
Can Gerrymandering Be Stopped?
The fixes that exist are state by state. A federal ban on partisan gerrymandering passed the House in 2022 as part of the Freedom to Vote Act and died in the Senate (Brennan Center).
Independent commissions take the pen away from sitting lawmakers. By the Brennan Center’s count, the independent commissions in Arizona, California, Colorado, and Michigan drew 19% of congressional districts but 41% of the districts rated toss-ups in 2024.
Commissions in four states drew about one in five districts and about two in five of the toss-ups.
The four commissions are built from citizens, not officeholders (All About Redistricting):
- Arizona: five members, two Democrats, two Republicans, and an independent chair. Created by voter initiative in 2000.
- California: 14 members, five Democrats, five Republicans, and four others. Created by voter initiatives in 2008 and 2010.
- Colorado: 12 members, four Democrats, four Republicans, and four unaffiliated. Created by voter-approved amendments in 2018.
- Michigan: 13 members, four Democrats, four Republicans, and five unaffiliated. Created by voter initiative in 2018.
In California and Michigan, adopting a map takes votes from Democratic, Republican, and unaffiliated members, so no single faction can push one through (Michigan has a fallback procedure if no map wins that mix). Commissions have limits. Virginia’s commission of legislators and citizens deadlocked in 2021, leaving the state supreme court to draw the map. California voters set their commission’s map aside for 2026 to answer the Texas redraw. New York’s legislature can override its commission by a supermajority.
Other fixes: state constitutional bans on partisan maps that state courts enforce, rules against mid-decade redrawing, and Iowa’s model, in which nonpartisan legislative staff propose maps drawn without political data and lawmakers vote on those proposals. In 2021, Iowa’s legislature rejected the first set and passed the second (All About Redistricting).
Which Party Gerrymanders More
Whichever party holds the pen, and after the 2020 census Republicans held it in far more states. The Brennan Center found that the maps used in the 2024 election had on average a net 16 fewer Democratic or Democratic-leaning districts than maps meeting strong anti-gerrymandering standards would have. It also notes that Republicans “weren’t alone”: Democrats in Illinois redrew the state’s map to leave Republicans just 3 of 17 seats (Brennan Center).
The 2026 redraws show both sides at work. The new maps were designed to shift 15 seats toward Republicans and 6 toward Democrats, with the details in the table above.
What Gerrymandering Does Not Explain
- Lopsided races are not all gerrymandering. In 2024, 84% of House seats were decided by 10 points or more, and only 9% by fewer than 5 (FairVote). Where voters live matters too. Justice Kagan’s Rucho dissent notes that Republicans win about 35% of the statewide vote in Massachusetts, but because they are spread evenly, ordinary maps consistently produce an all-Democratic delegation.
- Redistricting is required; gerrymandering is a choice. Every state with more than one House seat has to redraw after the census so districts have equal populations. The redistricting explainer covers that process.
- Majority-minority districts are not gerrymanders by default. Districts drawn so that a community of color can elect its choice were a core remedy under the Voting Rights Act. Whether a specific one crossed the line is what Callais was about.
- Both parties do it. The national tilt favors Republicans because they drew more maps after 2020, not because only one party gerrymanders.
Frequently Asked Questions
What is the purpose of gerrymandering?
To win more seats than your share of the vote. Mapmakers pack the other side’s voters into a few districts and crack the rest across many, so one party wins most districts by safe margins and loses a few by large ones. It can also be used to weaken the voting power of a group of voters.
Is gerrymandering legal?
Partisan gerrymandering is effectively legal under federal law, because the Supreme Court ruled in Rucho v. Common Cause (2019) that federal courts cannot judge it. Racial gerrymandering is still unconstitutional, but it has become harder to prove. State constitutions and state courts are where most remaining limits on partisan maps live.
Which party gerrymanders more?
Whichever party controls the map. After the 2020 census, Republicans controlled redistricting in far more states, and the Brennan Center found the maps used in 2024 had on average a net 16 fewer Democratic-leaning districts than fair maps would. Democrats drew aggressive maps too, including Illinois. The maps redrawn for 2026 were designed to shift 15 seats toward Republicans and 6 toward Democrats.
What is the difference between redistricting and gerrymandering?
Redistricting is the required redrawing of district lines, usually after each census. Gerrymandering is redistricting done to favor a party or weaken a group of voters.
How can I tell if my district is gerrymandered?
Not by its shape. Compare the statewide vote with the seats each party won over several elections, or look up your state’s map in PlanScore or the Princeton Gerrymandering Project’s report card, which grade maps on partisan fairness.
Why is it called gerrymandering?
It is named for Elbridge Gerry, the Massachusetts governor who signed an 1812 map with a salamander-shaped district. A newspaper cartoon combined his name with the salamander.
What You Can Do
- Find out who draws your state’s map. The state finder on the redistricting page shows whether your legislature, a commission, or no one draws it, and whether your state redrew for 2026.
- Vote in state supreme court and legislative races. Since Rucho, state courts are the only courts that can strike down a partisan map, and the legislature usually holds the pen. These races draw low turnout, so a small number of votes decides them.
- Testify when maps are drawn. Legislatures and commissions hold public hearings before they adopt maps. Common Cause tracks hearings and helps residents submit testimony about their communities.
- Back the groups in court. Campaign Legal Center, the NAACP Legal Defense Fund, and the Brennan Center bring most redistricting cases.
- Ask your state legislators to create an independent commission. Use the letter and call script below.