Which States Will Gain or Lose Seats in the Next Congress

The new census numbers are in, and they show an America continuing its long population shift from the Northeast and Midwest to the South and West, a trend that will shape Congress for the next decade.

The country’s old center of political power — the industrial belt stretching from New York to Illinois — is once again losing seats in Congress while Sun Belt states such as Florida, North Carolina and Texas will gain them. California will lose a seat for the first time.

Several of the states gaining or losing seats are key swing states, and the changes to the political map will help determine which party holds majorities in the House through the 2020s, beginning with next year’s midterm elections.

Most of the congressional district lines will be drawn in the upcoming months by state legislatures and local commissions that have been given redistricting authority. Republicans control the redistricting process in far more states than do Democrats, because of G.O.P. dominance in down-ballot elections.

Democrats, meanwhile, have shifted redistricting decisions in states where they have controlled the government — such as California, Colorado and Virginia — to independent commissions intended to create fair maps.

Congressional apportionment is determined by essentially dividing the U.S. population by 435, the number of seats in the House. The fastest-growing states will add new seats, while those that are shrinking or growing slower than the national average will lose them.

Republicans will need to flip only about five House seats in the 2022 election to seize control of the chamber.

The results released on Monday show that seven states will lose seats while six will gain. Texas will add two seats and Florida one. The fast-growing states of Montana and Oregon will each add one seat, as will Colorado and North Carolina. Montana’s second seat comes after 30 years of having just a single at-large district.

At the same time, the big states of the Midwest and Northeast that historically have backed Democrats will lose congressional seats and the electoral votes that come with them. Illinois, Michigan, Ohio, New York, Pennsylvania and West Virginia will each lose one district. California’s loss of one seat reflects the slowing population growth of the nation’s largest state.

If the 2020 election was re-run with the new Electoral College numbers, President Biden would have won 303 electoral votes, instead of the 306 he took last November. Mr. Biden won the Electoral College with plenty of votes to spare.

The census was hampered or delayed by an array of Trump administration efforts to remove undocumented immigrants from the count, a shift that mostly likely would have increased the number of Republican-held districts in the next Congress.

Who wins?

The fastest-growing states are the obvious winners. Texas has added multiple seats in each census since 1970, and Florida has added seats after each census since 1890.

No state has been gaining more people than Texas. In the last decade, Texas has effectively increased its size by the population of Connecticut — primarily because of the swarms of Americans and new immigrants moving en masse to its booming metropolitan areas surrounding Austin, Dallas and Houston.

Having more members of Congress means more political power for the growing states of the South and West. And having more electoral votes will highlight the priorities of these states in presidential contests — especially battlegrounds like Florida and Texas — and draw greater attention from the candidates.

Before the 1910 census, the number of congressional seats increased as the population grew. Since 1910, the number of House seats has been capped at 435. Gaining more seats means grabbing more political power from other states.

In the last five reapportionments, Texas has added 11 congressional districts, reaching 38 beginning with the 2022 election from 27 in 1990. Just 10 other states have more members of Congress than Texas has added in that period alone.

Who loses?

That certain states are losing seats is predictable, based on historical performance. New York has now lost congressional seats for eight reapportionments in a row. Pennsylvania has lost seats after every census since 1920. Ohio and Michigan have both lost seats five times in a row. West Virginia has lost two-thirds of its congressional districts since it had six heading into the 1960 census.

But losing a seat is a new experience for California, which doubled in population between the start of World War II and the turn of the millennium.

From 1860 to 2000, California gained congressional seats after every census. It kept the same number of seats, 53, after the 2010 census. Now the Golden State will lose one, yet another indication that its political influence may have plateaued.

Never has the New York House delegation carried less weight than it will after the 2022 election. After losing one seat, New York will have 26, down from a high of 45 in the 1930s and 1940s. The state’s loss was narrow — if it had counted just 89 more people, Minnesota would have lost a seat instead of New York.

New York has not had so few members of Congress since the 1800 census, when the House had only 142 members — less than one-third its current size.

Like New York, Pennsylvania is long past its high point of influence on Congress.

The 2020 census is the 10th in a row in which Pennsylvania has lost congressional seats.

Will more power shift to Republicans?

Republicans control the mapmaking process in key states like Florida, North Carolina and Texas, where there are new House seats to be created amid booming suburban populations. The G.O.P. is also likely to eliminate a Democratic district in Ohio, which will lose one seat.

At the same time, Democratic lawmakers in Illinois and New York are poised to eliminate Republican seats as they draw new maps.

And several key states with changes coming to their maps — California, Colorado, Michigan and Montana — have independent commissions tasked with determining new legislative boundaries on a nonpartisan or bipartisan basis.

“The parties have this natural inclination to go for broke, say, ‘We’ve got a new seat, let’s grab it and take the opportunity we have,’ ” said Bernard Grofman, a political science professor at the University of California, Irvine, who has served as a special master for court-ordered redistricting in multiple states. For Republicans, he said, “picking up new seats and stopping Joe Biden is going to have a high, high priority, even though they may pay a big political price down the road.”

The 2021 redistricting process will also be the first time since 1961 that a raft of mostly Southern states will not have their maps subject to a preclearance process from the Justice Department, following the Supreme Court’s 2013 decision to strike down Section 5 of the Voting Rights Act. The court last month heard arguments that could undo more elements of the act that would impede the ability to sue to block new maps.

Without having to seek preclearance, Republicans in states where they control all levers of government — Florida, Georgia and Texas, to name three — will have far more influence on the new maps than they have had in past reapportionment cycles.

A handful of states with split control of the government — including Minnesota, Pennsylvania and Wisconsin — will have a battle between Republican legislators and Democratic governors. In North Carolina, Republicans who control the legislature will draw the maps, which by state law cannot be vetoed by Gov. Roy Cooper, a Democrat.

In Texas, it’s likely its new districts will need to include at least parts of greater Houston, given the region’s population boom. Republican mapmakers will be hard-pressed to draw all the new districts in their favor, given how many Democratic voters live in and around the state’s largest population centers.

All districts within a state are supposed to have roughly the same population. The map below shows which districts have grown more or less than that number since redistricting after the 2010 census release.

The new Texas map presents the biggest question for partisan mapmakers: Whether to maximize their advantage heading into the 2022 midterm elections or draw fewer, more durable districts for Republicans.

Take a look at the full census data released Monday.