Illinois had the biggest decrease in population according to a new report from the Census Bureau.

Between July 1, 2013 to July 1, 2014, the state lost 9,972 people. On the other end, Texas saw the largest population increase adding more than 450,000 people during that time.

Cook County saw a very slight decrease in population. It’s one of four counties with a population of more than 1 million to experience a decrease. Others include industrial counties like Wayne County, Michigan; Cuyahoga, Ohio; and Allegheny, Pennsylvania.

The rate of people leaving Cook County for other counties has been increasing since 2012. More than 48,600 people left over the 2013-2014 timeframe.

P.S. Sriraj is an associate professor at the University of Illinois at Chicago.

He says in the past, people of low income populated in the city center, like Chicago. Now, that population is moving out to the suburbs and collar counties.

“Those reasons are typically tied to employment—proximity to employment. Could also be tied to crime, crime rate in the city versus the suburbs. And it’s also a direct correlation to quality of education,” he said.

Kendall and Will counties saw some of the biggest population gains in the state.

The birth rate has decreased in Cook County, while the death rate increased. Yet Cook County’s overall population has held mostly steady. That’s in part due to the number of people migrating here from other countries. More than 48,600 people immigrated to Cook County from other countries last year.

“If you look at the pattern of immigrants coming to the country, their first stop has always been the larger city,” Sriraj said. “Once they acclimatize to the culture and surroundings, they find a foothold in suburban locations. That’s typical.”

He says those international arrivals could eventually be part of that exodus to the collar counties.

Overall, across Illinois, more counties dipped in population than gained. Metro areas with the highest unemployment rate, like Decatur, Danville, Kankakee and Rockford, also saw the highest population decrease for the state.

Susie An is a WBEZ reporter. Follow her @soosieon.