Jefferson County is located in the eastern portion of Missouri and is part of the St. Louis Metropolitan Statistical Area. The county seat is Hillsboro. The county was organized in 1818.

Jefferson County is part of the St. Louis, MO-IL Metropolitan Statistical Area. It is located along the Mississippi River and is home to many parks, trails, and historic sites. The county is also home to the Jefferson National Expansion Memorial, which includes the Gateway Arch.

The county is governed by a three-member County Commission, which is elected in staggered four-year terms. The other elected officials are the County Assessor, County Collector, County Clerk, Prosecuting Attorney, Sheriff, and Treasurer.

For the most up-to-date and in-depth information, please check the public records links below.