SANTA BARBARA, Calif. — California's population shrank last year, the first time in its 171-year history that the nation's most-populous state has seen a decline in the number of people living here.

The state Department of Finance reported Friday that the population dropped by 182,083 people, or 0.46 percent, between Jan. 1, 2020, and the end of the year. The agency attributed the decline to out-of-state migration, slower international immigration and the coronavirus pandemic, which has killed nearly 61,000 residents at a time when the state is recording among the lowest birthrates in the nation.

The numbers serve as a kind of postscript to data released last month by the U.S. Census Bureau, which showed that California grew 6.1 percent over the last decade. The growth rate, lower than the national average, will cost the state one of its 53 congressional seats during reapportionment, another state first.

“Driven largely by a declining birthrate, the state’s population growth slowed in recent years and essentially hit a plateau,” said H.D. Palmer, the Department of Finance’s deputy director and chief spokesperson. “What’s temporarily tipped us into negative territory over the past year is deaths caused by covid, combined with the impact of immigration policy.”

California has been a national and international destination for much of the last half-century. After decades of double-digit population increases, the state’s growth rate peaked at 37 percent after the 1990 Census.

The state’s population growth has ebbed and flowed since then. The trends mostly have been driven by economic factors, from the exodus that followed the post-Cold War contraction of the defense and aerospace industry to the magnetic pull of the early dot-com era.

But growth has slowed significantly over the last decade, particularly in recent years. High housing costs have been the catalyst for a massive in-state migration of residents heading east in search of a lower cost of living away from the expensive Pacific Coast.

The new state figures add detail and depth to several trends that the census did not fully capture since the national count ended in April 2020.

For one, the trend of more Californians leaving the state than new residents arriving accelerated, as the year ended with a net annual exodus of 310,918 people. Almost 727,000 left California last year alone, according to the agency’s data.

Only twice in the past three decades has California reported an annual net increase in people arriving from other states. Those years — 1999 and 2000 — coincided with the start of the tech boom, which drew tens of thousands of people to Silicon Valley and the wider Bay Area.

But the current exodus has become part of the argument over deep-blue California’s political direction and whether its tax and regulatory policies are driving residents away.

A study published this week by the nonpartisan Public Policy Institute of California found that the state “has been losing lower- and middle-income residents to other states for some time while continuing to gain higher-income adults.”

“In the past five years the flow of middle-income residents out of the state has accelerated,” the study found.

The institute also reported that “people who move to California are different from those who move out.”

“In general, those who move here are more likely to be working age, to be employed, and to earn high wages — and are less likely to be in poverty — than those who move away,” the study found. “Those who move to California also tend to have higher education levels than those who move out — an especially important factor given the state’s strong need for college graduates.”

The state Finance Department attributed the annual population decline to lower-than-usual international immigration to California. State officials have cited the pandemic and the Trump administration’s immigration policies, which emphasized border protection and placed stricter limits on legal immigration, as reasons for the slowdown.

State officials also point to the pandemic as a chief cause of the decline. An estimated 51,000 California residents died of covid-19 in 2020, contributing to a death rate that was 19 percent higher than the average of the previous three years. Higher-than-average death rates were reported in all but seven of the state’s 58 counties.

“As the pandemic recedes and as immigration policies change, we expect we’ll be back to slightly positive growth by this time next year,” Palmer said.