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 given its name because it is halfway between Lower Lake and Calistoga which is 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 on the stagecoach route over Mt. St. Helena from Calistoga to Lower Lake . The first house was built at the site by J.H. Berry in 1870 . The town began in 1871 . The Middleton post office opened in 1871 and changed its name to Middletown in 1875 . Middletown enjoyed a robust quicksilver ( mercury ) mining industry through the end of the 19th century . By the early 1900s , cattle and sheep ranching were prominent , along with some limited pear and walnut production . A resort economy sprung up around the various natural springs , and the area around Middletown attracted vacationers from the Bay Area through the 1950s . As travel costs decreased , tourism to the resorts diminished as patrons were able use air travel to vacation in more far-flung places . Many of the resorts closed in the 1960s . In the 1970s and early 1980 , exploitation of nearby geothermal energy resources brought an influx of workers into the local economy . Electrical power 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 nearby Hidden Valley Lake enjoyed a population boom as commuters moved to the Middletown area looking for affordable housing ; keeping their jobs 50 to 100 miles away in Santa Rosa , Napa , and San Francisco . Middletown is currently populated primarily by commuters and retirees , enjoying a modest tourist trade based primarily on Harbin Hot Springs and the Twin Pine Casino located on the local Rancheria south of the town
Valley Fire
Valley Fire
Middletown, California