Legislative Redistricting: How Do States Draw Congressional Districts?
The U.S. census is a constitutionally mandated population count carried out by the federal government every 10 years. Census data offers invaluable insight into the changing demographics of eligible voters and population shifts among the states. The U.S. census also begins the congressional reapportionment and redistricting process, which plays a significant role in the congressional balance of power for the next decade to come.
In this article, we examine how congressional reapportionment and redistricting after each census affects the makeup of the U.S. House of Representatives for the following decade, and how the evolving demographics of eligible voters will continue to shape elections.
To create a lobbying and public affairs strategy that withstands political change, public affairs professionals need to understand how all the moving pieces fit together. The right public affairs software can help public affairs professionals implement a strategic approach to public policy with the latest news, expert analysis, and tools to inform their next move – including comprehensive congressional directories to help build the right relationships with key lawmakers and advance policy goals.
[Download our report for five best practices to shape policy after an election. Post-Election Shuffle: What You Need to Drive Policy Wins.]
How often are congressional districts redrawn?
States typically redraw their congressional districts every 10 years, following the completion of the U.S. census. Typically, census data is published at the end of year in which a count takes place. The most recent U.S. census was carried out in 2020. However, due to the Covid-19 pandemic, the 2020 census results were delayed until April 2021.
The next census will take place in 2030, and states will begin the redistricting process again in 2031.
States will occasionally update their districts in between the processes that occur every decade. For example, Alabama and Louisiana used new lines in 2024 following court orders, and lawmakers in North Carolina and New York made adjustments to their map. Ohio plans changes in 2025.
Why are congressional districts redrawn?
Population changes in the census count affect both the number of congressional districts a state has as well as the size and shape of those districts. The U.S. House of Representatives has a fixed number of 435 total seats, which are divided among the states to create congressional districts with roughly even populations.
Reapportionment – the redrawing of congressional district boundaries to reflect population changes – is a zero-sum game. For one state to gain representation, another must lose. Senate representation is unaffected by population changes as each state has two members.
How are congressional districts determined?
- After each census count, the Census Bureau provides states with initial population numbers.
- The bureau provides states with block-by-block population counts. These census blocks are areas bound by visible features, such as roads and railroads, and invisible boundaries, such as property lines and county limits.
- State mapmakers use the census blocks to redraw congressional districts of equal population size to account for population fluctuations.
As of April 1, 2020, the total U.S. population for apportionment was 331,108,434. Although it can vary, the average House district now represents 761,169 people – up from 710,767 in 2010.
States must comply with the federal Voting Rights Act and ensure that their newly drawn congressional boundaries don’t adversely impact voter representation based on race or ethnicity. Depending on the state, additional rules or criteria may also apply.
[Download our Voter Demographics and Redistricting report for a deep dive into the latest census demographic data – including race, income level, and education level – and how they relate to party affiliation.]
Who draws congressional districts?
States create their own processes for redrawing congressional districts. In most states, the state legislature controls the redistricting process. However, some states – such as Washington, California, and Arizona – use independent or bipartisan commissions.
When it comes to drawing new congressional boundaries, partisanship reigns supreme: 28 states put their legislative bodies in charge of drawing new congressional maps after the 2020 census. At that time, Republicans controlled the legislatures and therefore had final authority over district maps in 20 of those states, whereas Democrats controlled boundary-making in just eight states. This political advantage likely played a role in the Republican party netting several congressional seats in subsequent elections, according to Bloomberg Government Senior Elections Reporter Greg Giroux.
Greg Giroux
Senior Elections Reporter, Bloomberg Government
Redistricting and gerrymandering
Because redistricting plays a key role in election outcomes for the following 10 years, the process can quickly create partisan clashes and spur ongoing litigation as state political parties attempt to redraw district lines in their favor.
Republican- or Democratic-controlled legislatures can influence how the district boundaries are drawn to give their party the advantage. This process can lead to gerrymandering, which involves partisan mapmakers drawing districts that strongly favor their party by diluting the voting power of their opposition’s supporters, either by dividing those voters across several districts or crowding them all into a single district.
Although states redraw congressional districts every 10 years, courts may invalidate maps within that 10-year span and impose new boundary lines or direct legislatures to do so. This happened in 2011 in Florida, Virginia, North Carolina, and Pennsylvania.
The path to independent commissions
Establishing bipartisan commissions to draw congressional districts is an increasingly popular means of shifting redistricting power away from partisan legislatures.
Since 2020, six more states have adopted new systems for drawing congressional boundaries to force bipartisan consensus and improve the redistricting process. Different states have implemented various models, with specific appointee selection criteria and mapmaking processes.
For example, Arizona established an independent redistricting commission in 2000 to end gerrymandering practices. Arizona’s bipartisan commission is made up of five members: State lawmakers appoint two Democratic and two Republican commissioners from a pool of applicants, and that cohort of four partisan members selects an independent chair. Although Arizona lawmakers play a role in selecting commissioners, they don’t get to vote on or approve updated congressional maps.
The impact of the 2020 census on redistricting and elections
Congressional maps drawn by state legislatures and commissions after the 2020 census have had an ongoing impact on election outcomes since, including the shifting balance of power in the House.
[Download our Voter Demographics and Redistricting report for an in-depth analysis of the latest census data and how population changes will affect elections.]
Which states gained or lost congressional seats?
After reapportionment due to population changes in the 2020 census, six states gained House seats and seven lost them.
States that gained House seats from the 2020 census
- Colorado (+1 seat)
- Florida (+1 seat)
- Montana (+1 seat)
- North Carolina (+1 seat)
- Oregon (+1 seat)
- Texas (+2 seats)
States that lost House seats from the 2020 census
- California (-1 seat)
- Illinois (-1 seat)
- Michigan (-1 seat)
- New York (-1 seat)
- Ohio (-1 seat)
- Pennsylvania (-1 seat)
- West Virginia (-1 seat)
How interstate migration affected reapportionment
The reapportionment following the 2020 census reflects notable demographic shifts and new areas of population growth and decline. For example, the Sun Belt states benefited from booming Latino populations as well as from new residents relocating there from more liberal states, such as New York. Texas was the only state to gain two seats. Notably, California lost a congressional seat for the first time ever. New York lost a congressional seat after falling short by just 89 residents – however, it had been in danger of losing two seats.
Your congressional connection
Congressional redistricting reshapes the political landscape every 10 years, creating new challenges and opportunities for public affairs professionals. Navigating these changes requires up-to-date knowledge of key players, evolving constituencies, and shifting priorities in Congress. Comprehensive congressional directories support effective government relations by providing critical contact information and actionable insights that empower government affairs teams to build and maintain the relationships that drive advocacy efforts.
The right public affairs software is essential to implementing a strategic approach to public policy. Request a demo to learn more about how Bloomberg Government’s all-in-one platform can help you stay ahead of the curve in an ever-changing political environment.