Congressional Districts Explained

The total number of House seats (435) is fixed by law and does not change. After each decennial census, the Census Bureau determines each state's population, and the 435 seats are redistributed proportionally — a process called reapportionment.

The formula used is the Method of Equal Proportions (also called the Huntington-Hill method), a mathematical formula that minimizes the percentage difference in representation between any two states. Every state is guaranteed at least one seat — so even the least-populated state (Wyoming, ~580,000 people) gets a full representative. Because of this floor, the effective district size varies somewhat between states.

States that grow faster than the national average gain seats; states that grow more slowly — or lose population — lose seats. The political consequences are significant: seats shift from states with Democratic-leaning urban populations (New York, California, Illinois) to faster-growing states (Texas, Florida) that have recently trended Republican.

Once seats are apportioned to states, each state must draw the actual boundaries of its congressional districts. How this happens varies dramatically by state. In most states, the state legislature draws the maps — and the party in power draws them to its advantage. This process is called gerrymandering.

A growing number of states have moved to independent redistricting commissions — bodies designed to be insulated from direct political control. These commissions have produced somewhat more competitive maps, though no process eliminates partisan influence entirely.

The 2023 North Carolina Supreme Court reversed its own earlier ruling and allowed the Republican legislature's map to take effect for 2024 — flipping several previously competitive seats to safely Republican. In New York, after the court-imposed map of 2022, Democrats drew a new map for 2024 that reversed several Republican gains from 2022. These late-cycle map changes illustrate how much redistricting litigation shapes the House map.

Of the 435 House seats, the vast majority are effectively decided in the primary — not the general election. In safe Democratic districts (heavily urban, diverse, coastal), the Democratic primary is the real election. In safe Republican districts (rural, suburban South and Midwest), the Republican primary determines the winner.

This concentration of competition in a tiny fraction of seats has major consequences for American politics. Members from safe seats face primary challenges from their party's base rather than general election pressure from moderates. This incentivizes ideological polarization — Democrats in safe seats move left, Republicans in safe seats move right — because the only election that matters is the primary.

The most competitive House districts in 2026 are concentrated in:

• New York suburbs — Long Island, Hudson Valley, Staten Island (4-5 seats flipped between 2020-2024)
• California coastal suburbs — Orange County, LA suburbs, Central Valley border (CA-13, CA-27, CA-45, CA-47)
• Pennsylvania swing districts — Philadelphia suburbs and Lehigh Valley (PA-07, PA-08)
• Michigan — Detroit suburbs, western Michigan (MI-07, MI-10)
• Arizona — Phoenix suburbs (AZ-01, AZ-06)
• Virginia — Northern Virginia suburbs (VA-07)

Redistricting is not unlimited. Two major legal constraints apply to all congressional maps.

Equal population ("one person, one vote"): Under Supreme Court rulings going back to Wesberry v. Sanders (1964), congressional districts within a state must be as close to equal in population as practicable. For congressional districts, this standard is very strict — courts have struck down maps with even small population deviations if they were not justified by legitimate state interests.

Voting Rights Act (VRA): Section 2 of the VRA prohibits drawing maps that dilute the voting power of racial minorities. In states with large Black, Hispanic, or Native American populations, mapmakers must consider whether minority voters have an equal opportunity to elect representatives of their choice. This requirement has produced majority-minority districts — districts intentionally drawn to give a racial minority group a voting majority. In 2023, the Supreme Court in Allen v. Milligan upheld the VRA requirement that Alabama create a second majority-Black congressional district, reversing a lower-court-approved map.

What courts cannot do: The Supreme Court ruled in Rucho v. Common Cause (2019) that federal courts have no authority to hear claims of partisan gerrymandering — only racial gerrymandering claims are justiciable in federal court. Some state courts apply their state constitutions to partisan gerrymanders; others (like the reconstituted North Carolina Supreme Court in 2023) have reversed course.