New London County is among the 52% of counties nationwide that saw a decrease in population from 2010 to 2020 and, like the rest of the United States, became more racially diverse, according to data the U.S. Census Bureau released Thursday.

The bureau in April released statewide data, showing that Connecticut's population increased 0.9% over the decade to 3,605,944 residents, and on Thursday released more localized data that will be used for redistricting. Connecticut isn't losing or gaining any congressional seats, but the new data will impact borders for congressional and state legislative districts.

The U.S. population increased 7.4% since 2010, which Marc Perry, senior demographer in the Population Division at the U.S. Census Bureau, noted was the slowest growth since the 1930s.

Of Connecticut's eight counties, five saw their population shrink, including New London County, which lost 2%, or 5,500 people, for a total population of 268,555.

Population increased by 4.4% in Fairfield County, 0.6% in Hartford County and 0.3% in New Haven County.

New London County is the fifth-most densely populated county in the state, with 403.8 people per square mile.

According to a spreadsheet compiled by the nonprofit DataHaven, the population change in New London County ranged from a 7.54% decrease in Bozrah to a 2.41% increase in Ledyard. The population decreased by 4.25% in Groton, 0.92% in New London and 0.91% in Norwich.

"I am encouraged by the release of detailed data from the Census Bureau today, which showed that Connecticut gained 31,847 residents and that the population of all 3 of our largest cities grew over the past decade," Lt. Gov. Susan Bysiewicz said in a statement, referring to Bridgeport, Stamford and New Haven.

Bysiewicz, who served as chair of Connecticut's Complete Count Committee, touted the state's 99.9% overall response rate and 70.6% self-response rate, which increased from 2010.

Mark Abraham, executive director of DataHaven, said one thing that was surprising was how much some of the city centers in Connecticut grew. He noted that this is consistent with the national trend of people leaving smaller towns for larger urban areas.

"The country's population is increasingly metropolitan," Perry said in a news conference Thursday. He said the 10 largest cities in the country all grew this past decade, and eight of them grew at a higher rate than the decade before.

Abraham also said with Connecticut's aging population, it's striking to see how the adult population is increasing but the child population is decreasing. From 2010 to 2020, the adult population of New London County increased by 2,466 people, while the child population dropped by 7,966.

Abraham doesn't expect legislative districts in the county to change much, considering none of its municipalities saw dramatic population changes. But he said some Senate districts in eastern Connecticut may stretch west, since the growth in Fairfield County means more districts will need to be added there.

While the population living in group quarters increased in 31 states, Connecticut was one of only six states where this population decreased by 5% or more. Group quarters include college housing, nursing homes, group homes, military barracks and correctional facilities.

The Census Bureau will release its redistricting in easier-to-use formats by Sept. 30.

Growing more racially diverse

"The U.S. population is much more multiracial and more racially and ethnically diverse than what we measured in the past," said Nicholas Jones, director and senior adviser of Race and Ethnic Research and Outreach at the Census Bureau.

One such metric is the Diversity Index, which measures the probability that two random people will be from different racial and ethnic groups. Nationwide, this figure increased from 54.9% in 2010 to 61.1% in 2020.

It increased from 46.4% to 55.7% in Connecticut and from 37.4% to 45.3% in New London County, giving the county a diversity index rank of 1,062 out of 3,143 counties.

The non-Hispanic white population decreased by 10% statewide and by 9% in New London County, while the Hispanic population increased by 30.1% statewide and 33.2% in the county. The Black population increased by 7.7% statewide and decreased by 0.46% in the county.

Statewide, 63.2% of the population is white, and the second largest racial or ethnic group is Hispanic or Latino, at 17.3%.

e.moser@theday.com