Built in 1825-1828, the Lancaster County courthouse was designed by Robert Mills of Charleston, South Carolina, America's first native born, professionally trained architect, State Civil and Military Engineer, and designer of the Washington Monument. In 1792, John Simpson gave a courthouse site to the people of the region known as Lancaster County from 1785 to 1798, Lancaster District from 1798 to 1868, and Lancaster County since 1868. Three courthouses have occupied the site: a log house from 1795 to 1800, a frame building from 1800 to 1828, and the present structure.