Jefferson County is the most densely populated county in the U.S. state of Alabama, the county seat being Birmingham. As of 2000 U.S. Census, the population of Jefferson County was 662,047. Jefferson County is the most populated and principal county in the Greater Birmingham area.
Jefferson County was established on 13 December 1819, from Blount County by the Alabama legislature. It was named in honor of Thomas Jefferson. The county is located in the north-central portion of the state, on the southern extension of the Appalachians, in the center of the iron, coal and limestone belt of the South. Jefferson County is bordered by Blount, Bibb, Saint Clair, Shelby, Tuscaloosa, and Walker counties. It encompasses 1,119 square miles. The county seat was at Carrollsville from 1819-21, at Elyton from 1821-73, and since 1873 has been at Birmingham, which was named for England's iron and steel center in Warwickshire.