The greater Chicago region was the only one of the 10 largest metropolitan areas nationwide that saw a population decrease between 2016 and 2017, according to just-released census data.

Chicago and the surrounding suburbs had a population of 9,533,040 in 2017, compared with 9,546,326 in 2016, the data from the U.S. Census Bureau shows. Chicago maintained its rank as the third most populous metropolitan region in the United States.

“This is the third year in a row the numbers have declined,” said Alden Loury, director of research and evaluation at the Metropolitan Planning Council. “It’s not normal for large areas to lose population. The fact that this is happening is a cause for concern.”

The Dallas-Fort Worth area saw the most growth with a 146,000-population increase.

The New York metropolitan area, ranked number one, had a population of 20,320,876 in 2017, compared with 20,275,179 for the previous year. The Los Angeles metropolitan region ranked second, with Dallas-Fort Worth coming in fourth for both 2017 and 2016.

Elsewhere, Cook County, the nation’s second most populous, saw the biggest drop — in percent — of any of the nation’s 10 most populous counties. Cook County’s population dropped by 20,093, from 5,231,356 to 5,211,263.

“By and large, this is a function of not very many people coming to Cook County and a larger number of people leaving,” Loury said. In addition to migration, births and deaths also factor into population change.

The 10 largest counties in the country all maintained their rank compared to last year. The only other county among the nation’s 10 populous to lose population was Kings County, N.Y., better known as the New York borough of Brooklyn. Brooklyn lost a population of 2,088.