Jefferson county was formed in 1780. It is located in the Outer Bluegrass region of the state. The elevation in the county ranges from 383 to 902 feet above sea level. In 2000 the county population was 693,604 in a land area of 385.09 square miles, an average of 1801.1 people per square mile. The county seat is Louisville. Jefferson was one of the original counties in the Kentucky territory of Virginia. It is the most populous county and the most densely populated county in the state.