Bond County, Ill.
Bond County is one of the two easternmost counties in the metropolitan area, with a population of 17,727. Although agriculture dominates the economy, Carlyle Lake is bordered by a variety of resort, hunting, and fishing businesses.
Calhoun County, Ill.
Calhoun County has a population of 5,048 and is located on a peninsula between the Mississippi and Illinois Rivers. Ferries are the major mode of transportation, and this county features many historic sites and nature areas.
Clinton County, Ill.
Just over 37,956 people reside in primarily rural Clinton County, with some resort-based industry surrounding the southern half of Carlyle Lake. Illinois State Highway 50 and parallel railroad tracks bisect the county east to west.
Jersey County, Ill.
Jersey County, population 22,916 is on the Great River Road, which winds alongside the Mississippi River. The county is largely rural, with small towns dispered throughout. Principia College, overlooking the Mississippi, is in the picturesque village of Elsah.
Macoupin County, Ill.
The northernmost county in the metro area is Macoupin County with a population of 47,687. Interstate 55 cuts across the southeastern edge of this agricultural county. The county seat is Carlinville.
Madison County, Ill.
The Mississippi River forms the western border of Madison County, whose population is 268,459. Much of the population and employment is centered in the county seat, Edwardsville, and other cities including Alton, Collinsville, and Granite City.
Monroe County, Ill.
Monroe County's major industry is agriculture. The county has easy access to the City of St. Louis via Interstate 255 and the Jefferson Barracks Bridge. Waterloo serves as the county seat for the 33,306 residents of the area.
St. Clair County, Ill.
Across the Mississippi River from the City of St. Louis, St. Clair County has a population of 270,259. Belleville is the county seat. The county is home to both MidAmerica St. Louis Airport and Scott Air Force Base.
Source: "Annual Estimates of the Resident Population for Counties 2011" U.S. Census Bureau.
Note: Population estimates are as of July 1, 2011.