The total population is 9.6 million. Chicago had the seventh-largest population hike in the country.
Kendall County was the nation's fourth-fastest growing county. Its population grew seven percent to 103,500 from 96,500. Three other Chicago-area counties -- DuPage, Lake and Will -- were among the country's 100 largest.
Cook County, home to Chicago, was the second-most populous county in the country, with 5.3 million residents.
Kendall County was the nation's fastest-growing county from April 2000 to July 2008, when it increased by 89.6 percent. Will County, south of Chicago, also made the list of fastest-growing during the same period, increasing by 35.6 percent.
Alexander County, in far southern Illinois, had the state's largest population decrease from 2000 to 2008, losing 15 percent of its population.
On the Net: Census Bureau: http://www.census.gov/
Illinois, specifically the Chicago area, had some of the largest and fastest-growing areas of the country as of last July, according to Census data released Thursday.
The following are July 1, 2008, population figures by area (July 1, 2007 figure in parentheses):
--Chicago-Naperville-Joliet metropolitan area: 9,569,624 (9,496,853)
--Cook County: 5,294,664 (5,271,405)
--DuPage County: 930,528 (926,228)
--Lake County: 712,453 (706,386)
--Will County: 681,097 (670,663)
Source: U.S. Census Bureau
The Associated Press contributed to this report.