LOS ANGELES — California is poised to lose a congressional seat for the first time in its history as a state, based on U.S. Census Bureau population estimates released Monday that showed the nation’s growth continued to slow in 2019.

Some 27 states and the District of Columbia lost residents through net domestic migration between 2018 and 2019, the new census data show.

About 203,000 people left California in that period, a result of the state’s shifting migration patterns and economic strains that are making it harder to afford living here. New York, Illinois, New Jersey, Massachusetts and Louisiana also saw large losses to other states.

California’s potential loss in reapportionment, which will be determined by next year’s census count, would drop the state’s number of seats in the U.S. House of Representatives from 53 to 52, said William Frey, a senior fellow at the Brookings Institution.

“It’s got a lot to do with dispersion from California to the rest of the west,” Frey said. “Arizona, Texas and Colorado are all big destinations for California migrants, and they all are gaining seats.”

A 2019 relocation study by Texas Realtors found that 63,175 Californians moved to Texas in 2017, while California was the top destination for Texans to move —nearly 41,000 relocated here.

Texas is likely to gain three seats following the 2020 decennial count, according to Frey’s analysis of census data, while states such as Arizona, Colorado and Oregon may gain one seat apiece.

The apportionment population count for each of the 50 states includes the state’s total resident population —citizens and non-citizens —as well as a count of the overseas federal employees and their dependents who have that state listed as their home state in their employers’ administrative records, according to the U.S. Census Bureau.

The House of Representatives is limited to 435 members, not under the U.S. Constitution, but because of a 1929 federal law that could be changed if lawmakers and the president agreed to do so.

Exactly where California would lose a seat in the House depends on which communities are larger or smaller compared to census numbers from 2010. The state’s Citizens Redistricting Commission, whose members will be selected in coming months, will hold public hearings in 2021 to determine how to redraw congressional maps.

Paul Mitchell, one of the state’s leading analysts of the redistricting process, said that two places could dominate the discussion: the communities sitting at the intersection of Los Angeles, Orange and San Bernardino counties and the suburbs to the east of San Francisco.

But other big changes to the political map-drawing process are also in store —including the 2013 ruling by the U.S. Supreme Court to strike part of the federal Voting Rights Act that strongly influenced the current California maps.

“That will allow a massive rewrite of the Central Valley congressional districts, so it might be really hard to see the total impact” of losing a House seat because of population, Mitchell said.

Even so, the most obvious political impact would be to force incumbent House members to either run against each other or leave office. In 2012, Rep. Brad Sherman (D-Northridge) defeated former Rep. Howard Berman in a bitter contest brought on by the new lines drawn in Los Angeles County.

California’s future numerical strength in Congress hinges in part on making sure that members of historically undercounted groups are included in the census count. In California, 72% of the population belongs to one of these groups, according to the Public Policy Institute of California.

State census workers, community organizations and local politicians started outreach efforts as early as April to ensure an accurate tally in next year’s count. In addition to reapportionment, nearly $800 billion in federal tax dollars and political redistricting are at stake.

State government leaders have allocated about $187 million to help verify addresses and expand outreach efforts, according to California’s census office.

Still, there will be major hurdles. Those without reliable internet connections may be missed in a census that will rely heavily on online surveys. Los Angeles County, officials say, will be the nation’s hardest to tally because of its high concentrations of renters and homeless people, as well as immigrant communities that may not participate, either because of language barriers or because they fear being targeted by federal immigration authorities.

“If, as many fear, non-citizen populations and the state’s heavily Latino population either fails to participate or participates without providing full household counts, then California could lose more than one seat,” said Mitchell, whose firm analyzes political data for regional and statewide candidates.

Nationally, natural increase (births minus deaths) has declined steadily over the past decade. The U.S. also registered a decline in its population under the age of 18, Frey, the demographer, said. California led in that category, with a drop of about 400,000 people under the age of 18, followed by Illinois and New York. The South and West saw the biggest gain in children, Frey added, led by Texas.

“This is a symptom of an aging population,” he said, “and in states like California, an out-migration of younger families with children.”

California’s representation stayed the same following the 2010 census count. If the state does lose a seat or two in 2020, Frey said, it’s uncertain whether the decline would carry into the 2030 count.

“In a way, these last few years are a confluence of things that may not continue over time,” he said. “The slowdown in immigration may not continue, millennials may finally start having kids. Domestic out-migration may continue. All those things happened at the same time, so I don’t think they’re going to be quite as dim in the next few years.”