Middletown is a census-designated place (CDP) in Lake County, California, United States. Its population was 1,323 at the 2010 census, up from 1,020 at the 2000 census. Middletown was firm its post because it is halfway along with Lower Lake and Calistoga, which is 17 miles (27 km) to the south. The town was severely damaged by the 2015 Valley Fire.

At one time, the community was known as Middle Station, and was a halfway point upon the stagecoach route higher than Mt. St. Helena from Calistoga to Lower Lake. The first home was built at the site by J.H. Berry in 1870. The town began in 1871. The Middleton publish office opened in 1871 and untouched its post to Middletown in 1875. Middletown enjoyed a robust quicksilver (mercury) mining industry through the fade away of the 19th century. By the to come 1900s, cattle and sheep ranching were prominent, along taking into consideration some limited pear and walnut production. A resort economy sprung up as regards the various natural springs, and the area around Middletown attracted vacationers from the Bay Area through the 1950s. Many of the resorts closed in the 1960s. In the 1970s and yet to be 1980s, exploitation of clear geothermal cartoon resources brought an influx of workers into the local economy. Electrical capability plants powered by “steam wells” were built in the mountains above Middletown. As housing prices in the Bay Area increased in the late 20th century, Middletown and easy to accomplish to Hidden Valley Lake enjoyed a population boom as commuters moved to the Middletown area looking for affordable housing. Nearby tourism includes Harbin Hot Springs and the Twin Pine Casino located on the local Rancheria south of the town. A large resort, 2 miles (3.2 km) southeast of town, was proposed in 2020, consisting of low-density residential development, preserved gain access to space, retail space, restaurants, and several boutique hotels.

On September 12, 2015, about half the town, including city blocks, commercial buildings and an apartment complex, was destroyed by the fast-moving Valley Fire. The town was directly in the alleyway of the advancing fire, and suffered a “devastating blow”.

The 2019 Kincade Fire started in Sonoma County and at some dwindling prompted mandatory evacuations in Lake County.