Franklin County, Mo.
Union is the county seat of Franklin County, which has an estimated population of 101,938. Manufacturing is the dominant industry, primarily in the city of Washington. Small farms and wineries also contribute to the economy.
Jefferson County, Mo.
Jefferson County, bordered on the east by the Mississippi River, has experienced rapid growth recently to 219,480. Manufacturing, construction, and business services are the major industries. Interstate 55 connects the county to Memphis, the City of St. Louis, and Chicago.
Lincoln County, Mo.
Lincoln County, whose county seat is Troy, is north of Warren and St. Charles Counties with the Mississippi River to the east. Manufacturing and service industries are major employers. The county is one of the fastest growing in the country with a population of 53,076, which increased by more than 37.9% from 2000 to 2008.
St. Charles County, Mo.
St. Charles County, with a population of 365,151, has been one of the fastest-growing counties in the country for decades. The county features a cross-section of industry, as well as extensive retail and some agriculture. St. Charles County has two small airports and two ferries that cross the Mississippi River.
City of St. Louis, Mo.
Home to an estimated 318,069 people within 61.9 square miles, the City of St. Louis is the most densely populated and industrial county in the metropolitan area. Manufacturing and corporate headquarters have a strong presence. Interstates 55, 70, 64, and 44 all pass through the city.
St. Louis County, Mo.
With 998,692 residents, St. Louis County is the most populous of the metropolitan-area counties. There is still some agriculture along the Missouri River in the north, but overall the area is thoroughly suburban with many corporate offices and service businesses. Clayton, the county seat, is often called the St. Louis area's "second downtown".
Warren County, Mo.
Warren County, population 32,515, is primarily agricultural. The Missouri River forms the southern border; Interstate 70 crosses the county east to west. Warrenton is the county seat.
Washington County, Mo.
Source: "Annual Estimates of Resident Population for Counties 2011", U.S. Census Bureau.
Washington County is primarily agricultural. This southernmost county in the metropolitan area is home to 25,076, with the county seat in Potosi.
Note: Population estimates as of July 1, 2011.