Jefferson County, Missouri

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Jefferson County is located in the eastern portion of the state of Missouri. It is a part of the St. Louis Metropolitan Area. As of the 2010 census, the population was 218,733, making it the sixth-most populous county in Missouri. Its county seat is Hillsboro. The county was organized in 1818 and named in honor of former president Thomas Jefferson.

Monroe County, Illinois St. Louis County, Missouri Franklin County, Missouri St. Francois County, Missouri Washington County, Missouri Ste. Genevieve County, Missouri City of St. Louis St. Charles County, Missouri St. Clair County, Illinois Randolph County, Illinois