The number of congressional districts (House seats) each state gets is determined every 10 years, after the nationwide population count known as the decennial census.

Core idea

  • The Constitution requires a national census every 10 years (in years ending in “0”), and that census is used to decide how many House seats each state receives, in a process called apportionment.
  • Federal law currently fixes the total number of House members at 435, so every 10 years those 435 seats are re-divided among the states based on updated population data.

Apportionment vs. redistricting

  • Apportionment : How many seats each state gets. This is done every 10 years, using the decennial census, and the clerk of the House must notify states of their number of seats by January 25 of the year after the census.
  • Redistricting : Once a state knows how many seats it has, it redraws its internal district lines so each district has roughly equal population; this also generally happens every 10 years, though courts can force changes in between.

Practical timeline example

  • 2020 census → population counted.
  • 2021 (early) → official apportionment numbers sent to Congress and to each state, telling them how many House seats they now have.
  • Following years → states redraw district maps, and the first elections using the new districts occur in the next even-year federal election (here, 2022).

Key takeaway

  • If the question is “how often is the number of congressional districts per state determined?” the answer is: once every decade, after each decennial census , through the apportionment process.

Information gathered from public forums or data available on the internet and portrayed here.