Gerrymandering is the practice of drawing electoral district boundaries to give one group an advantage over another. The goal is to shape who wins by deciding in advance which voters are grouped together. In the United States the term applies to congressional districts and to state legislative districts.
This guide covers where the word came from, the two techniques mapmakers use, the difference between partisan and racial gerrymandering, what the Supreme Court has and has not decided, real cases with dates and outcomes, and how to evaluate a map yourself.
Where the word comes from
On February 11, 1812, Massachusetts Governor Elbridge Gerry signed a bill redrawing the state senate districts. One district in Essex County had a long, curling shape, and a political cartoon published in the Boston Gazette on March 26, 1812 drew it as a winged creature under the title “The Gerry-Mander.” The name stuck.
Three details are worth getting right. The 1812 map redrew state legislative districts, not congressional ones. Nobody knows who actually coined the word: the Library of Congress states plainly that the person who coined it has never been identified. And Gerry pronounced his name with a hard G, as in Gary, so the modern soft-G pronunciation does not match the man it came from.
The Massachusetts Historical Society, which holds the original broadside, adds a caution: by modern standards the district was not especially misshapen. The cartoon simply worked. There is also little evidence that Gerry wrote the law or strongly supported it.
Packing and cracking
The Supreme Court described the two core techniques in Gill v. Whitford in 2018. Cracking means dividing a party’s supporters among multiple districts so that they fall short of a majority in each one. Packing means concentrating one party’s backers in a few districts that they win by overwhelming margins.
Both work by wasting votes. A vote is wasted when it goes to a losing candidate, or to a winning candidate beyond the margin needed to win. Packing wastes the surplus in districts already won. Cracking wastes votes in districts that keep coming up short. An earlier Court used different names for the same ideas, calling them stacking and splitting in Davis v. Bandemer in 1986.
For the arithmetic worked through step by step, see packing and cracking.
Partisan and racial gerrymandering are treated differently
Partisan gerrymandering means drawing lines to favor a political party. Racial gerrymandering means drawing them based on the race of voters. American law now treats these two very differently, and the gap has widened.
Racial claims run through the Equal Protection Clause of the Fourteenth Amendment and through Section 2 of the Voting Rights Act, codified at 52 U.S.C. 10301. Section 2 bars any voting practice that results in a denial or abridgement of the right to vote on account of race or color, judged on the totality of circumstances. The statute also says explicitly that it creates no right to proportional representation.
Partisan claims have a different fate in federal court, covered in the next section.
What the Supreme Court has and has not decided
The rules courts apply now come from a small line of Supreme Court decisions.
- Baker v. Carr (1962) held that apportionment claims can be heard in federal court rather than being political questions the courts must avoid.
- Reynolds v. Sims (1964) established one person, one vote, requiring seats in both chambers of a state legislature to be apportioned substantially on population.
- Shaw v. Reno (1993) recognized a claim where a district is so bizarre on its face that it is unexplainable on grounds other than race. The decision was 5 to 4 and sent the case back rather than striking the map itself.
- Miller v. Johnson (1995) set the test still used for racial claims: a plaintiff must show race was the predominant factor and that traditional districting principles were subordinated to it.
- Vieth v. Jubelirer (2004) produced a judgment of 5 to 4, but only four justices would have held partisan claims permanently non-justiciable. Justice Kennedy concurred separately and declined to foreclose future relief.
- Shelby County v. Holder (2013) struck the coverage formula in Section 4(b) that determined which jurisdictions needed federal preclearance. The Court said its decision did not affect the nationwide ban in Section 2.
- Rucho v. Common Cause (2019) held 5 to 4 that partisan gerrymandering claims present political questions beyond the reach of the federal courts.
- Allen v. Milligan (2023) declined to remake Section 2 and let an Alabama challenge proceed.
- Louisiana v. Callais (2026) substantially narrowed Section 2.
Rucho is the hinge. After it, a claim that a map is unfair to a political party cannot be won in federal court. The Court was explicit that this is not the end of the road, and pointed to state constitutions and state courts as an available forum. Rucho itself consolidated two cases, one challenging a Republican-drawn map in North Carolina and one challenging a Democratic-drawn map in Maryland.
Callais, decided April 29, 2026 by a vote of 6 to 3, changed the racial side. The Court held that Section 2 imposes liability only when the evidence supports a strong inference that a state intentionally drew districts to give minority voters less opportunity because of race. Illustrative maps offered by plaintiffs can no longer use race as a districting criterion, and plaintiffs must now show racial-bloc voting that cannot be explained by party affiliation. Section 2 remains on the books nationwide, and the burden of proving a violation is considerably higher than it was in 2023.
Three real examples
Pennsylvania, 2018. The congressional map enacted in 2011 by a Republican-controlled legislature was challenged by the League of Women Voters and eighteen voters. On January 22, 2018 the Pennsylvania Supreme Court held the plan clearly, plainly and palpably violated the state constitution, and the full opinion on February 7 grounded that in the Free and Equal Elections Clause. The court adopted a remedial map on February 19 after the legislature missed its deadline. This happened seventeen months before Rucho, and it is the clearest illustration of what a state constitution can still do.
Maryland, 2011 and 2021. Maryland’s Democratic-controlled legislature redrew the Sixth District in 2011, moving roughly 360,000 voters out and 350,000 in. Republican voters sued on a First Amendment theory. That case reached the Supreme Court and was disposed of alongside Rucho. When Maryland redrew again in 2021, a state court struck the new congressional plan on March 25, 2022 under the state constitution, and the legislature passed a replacement within days.
Illinois, 1991. The Fourth District in Chicago, often called the earmuffs district for its shape, is usually cited as a partisan gerrymander. A federal court drew it. After the 1990 census the legislature deadlocked, and a three-judge panel adopted a plan creating the state’s first Hispanic-majority congressional district, joining two neighborhoods separated by an expressway with a thin connector holding under five percent of the district’s population. A voter challenged it as a racial gerrymander. The district was upheld in 1997 and the Supreme Court summarily affirmed in 1998.
The pattern across these cases runs in both directions. Republican-drawn maps were struck in Pennsylvania, Democratic-drawn maps in Maryland, and the most notorious shape in the country was drawn by judges.
How to evaluate a map
No single number settles the question, and after Rucho no number can settle it in federal court. These measures still carry weight in state courts, where compactness and similar criteria are written into constitutions and statutes.
- Compactness. The Polsby-Popper score compares a district’s area to the area of a circle with the same perimeter. The Reock score compares its area to the smallest circle that encloses it. Both run from 0 to 1, and higher means more compact.
- Subdivision splits. Count how many counties, cities and towns the map divides. Repeated splitting of the same county is worth a closer look.
- The efficiency gap. Subtract one party’s statewide wasted votes from the other’s and divide by all votes cast. It was the centerpiece of the plaintiffs’ case in Gill v. Whitford, and the defense experts contested its reliability.
- Partisan symmetry. Ask how each party would fare if their vote shares were reversed. Justice Kennedy described this measure in 2006 and then declined to adopt it as a constitutional standard.
Shape alone proves little. Districts can look strange for legitimate reasons, including rivers, coastlines, reservations and the requirement to keep population equal.
Mid-decade map changes in 2025 and 2026
Redistricting normally follows the census once a decade. Since the summer of 2025, ten states have changed congressional maps between censuses, a rate the National Conference of State Legislatures says has not been seen since the 1800s: Alabama, California, Florida, Louisiana, Missouri, North Carolina, Ohio, Tennessee, Texas and Utah.
The routes differed. Legislatures acted in Texas, Missouri, North Carolina, Florida, Tennessee and Louisiana. California voters approved Proposition 50 on November 4, 2025, setting aside the state’s independent commission through 2030. Ohio’s backup commission reached a bipartisan agreement. A court ordered Utah’s map. Alabama reverted to its 2023 legislature-drawn map after the Supreme Court granted a stay on June 2, 2026. Other states tried and stopped, including Indiana, Virginia, South Carolina and Washington.
How to see your own district
Enter a ZIP code or a full street address in the lookup on the home page to see your district, your representative, and the boundary map. A full address is more exact, because a single ZIP code can cross district lines. You can also browse all 435 districts or read what a congressional district is.
Common questions about gerrymandering
What does gerrymandering mean?
Gerrymandering means drawing the boundaries of an electoral district to give one group an advantage. The word combines the name of Massachusetts governor Elbridge Gerry with the word salamander, after a district drawn in 1812 that was said to resemble one.
What is an example of gerrymandering?
The two standard techniques are packing and cracking. Packing concentrates opposing voters into a small number of districts so their votes are wasted on lopsided wins. Cracking splits them across many districts so they are outnumbered in each one.
Is gerrymandering legal in the United States?
Racial gerrymandering is prohibited under the Voting Rights Act and the Fourteenth Amendment. Partisan gerrymandering was placed beyond the reach of federal courts by the Supreme Court in Rucho v. Common Cause in 2019, so partisan claims are now heard in state courts under state constitutions.
Who draws congressional district boundaries?
Most states give the job to the state legislature. A smaller number use an independent or bipartisan commission. The method varies by state and determines who can be held accountable for a map.
How can I tell if my district is gerrymandered?
No single measure settles it. Analysts look at how compact a district is, whether it splits counties and cities without reason, and whether the statewide seat split matches the statewide vote share. A district that fails all three is worth a closer look.
How often are districts redrawn?
Congressional maps are normally redrawn once every 10 years after the census. Mid-decade redraws happen when a court strikes a map down or a legislature chooses to redraw, and 10 states saw such an effort in 2025 and 2026.
Sources
Definitions of packing and cracking come from the U.S. Supreme Court opinion in Gill v. Whitford and from Congressional Research Service report R45951. Case holdings and vote counts come from the published opinions of the Supreme Court of the United States. Section 2 text comes from 52 U.S.C. 10301. The 1812 origin comes from the Massachusetts Historical Society, which holds the original broadside, and from the Library of Congress. Pennsylvania comes from the opinions of the Supreme Court of Pennsylvania. Illinois comes from the federal district court decisions in Hastert and King. Mid-decade map changes come from the National Conference of State Legislatures redistricting tracker, updated August 11, 2026. Checked August 12, 2026.
Last updated September 9, 2026.
