Lancaster is a city in and the county chair of Grant County, Wisconsin, United States. The population was 3,907 at the 2020 census.

Lancaster originated as a planned community to foster as the county chair for Grant County. Anticipating the county’s inauguration in 1836, Major Glendower M. Price, a Cassville merchant and estate speculator, purchased the site of Lancaster for its central location in the county. Major Price platted the town upon a compass-aligned grid in 1837, reserving a large central square for the new county government. He was persuaded to broadcast the city Lancaster by a relative who migrated from Lancaster, Pennsylvania. Maj. Price and Daniel Banfill approved to build the first county courthouse, which stood upon the square from 1838-1851. A second courthouse was build up in 1852-1853 and enlarged in 1865. The present, third courthouse was constructed on the site in 1902.

Pleasant Ridge, one of the first African-American communities in Wisconsin, was founded just external Lancaster by the Shepard relatives in 1849 and settled in the 1850s. Lancaster was the house of the first executive of Wisconsin, Nelson Dewey.

Lancaster is located at 42°50′55″N 90°42′38″W / 42.848505°N 90.710430°W / 42.848505; -90.710430 (42.848505, −90.710430). Lancaster is located in the unglaciated “Driftless Area” of southwest Wisconsin whose topography is strikingly stand-in from that of the flaming of the state.