Duval County is located in northeastern Florida. Duval County was named for William Pope DuVal (Governor of Florida Territory from 1822 to 1834) when the county was formed in 1822. The original county stretched from the Atlantic Ocean to the Suwannee River, but today, the county contains 774 square miles of land area and 145 square miles of water surface. The county seat is Jacksonville.

In 1968, the Jacksonville municipal government was combined with the Duval County government but it was not a consolidated city/county thing as other incorporated cities in the county maintain their own municipal governments and services. Jacksonville did expand the city limits to encompass all the unincorporated areas of the county so that Jacksonville became the largest city in the United States in terms of land area.