Middletown is a census-designated place in Lake County, California. It sits at the elevation of 335 m. Its population was 725 at the 2020 census down from 1,323 at the 2010 census. Middletown was given its name because it is halfway between Lower Lake and Calistoga, which is 17 miles (27 km) to the south. The town was severely damaged by the 2015 Valley Fire.