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

Lancaster originated as a planned community to serve as the county seat for Grant County. Anticipating the county's establishment in 1836, Major Glendower M. Price, a Cassville merchant and land speculator, purchased the site of Lancaster for its central location in the county. Major Price platted the town on a compass-aligned grid in 1837, reserving a large central square for the new county government. He was persuaded to name the city Lancaster by a relative who migrated from Lancaster, Pennsylvania. Maj. Price and Daniel Banfill contracted to construct the first county courthouse, which stood on the square from 1838–1851. A second courthouse was constructed 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 outside Lancaster by the Shepard family in 1849 and settled in the 1850s. Lancaster was the home of the first governor 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 different from that of the rest of the state.

According to the United States Census Bureau, the city has a total area of 3.01 square miles (7.80 km), all of it land.

Historical population

Census	Pop.	Note	%±
1880	1,069		—
1890	1,543		44.3%
1900	2,403		55.7%
1910	2,329		−3.1%
1920	2,485		6.7%
1930	2,432		−2.1%
1940	2,963		21.8%
1950	3,266		10.2%
1960	3,703		13.4%
1970	3,756		1.4%
1980	4,076		8.5%
1990	4,192		2.8%
2000	4,070		−2.9%
2010	3,868		−5.0%
2020	3,907		1.0%
U.S. Decennial Census

As of the census of 2020, the population was 3,907. The population density was 1,298.9 inhabitants per square mile (501.5/km). There were 1,800 housing units at an average density of 598.4 per square mile (231.0/km). The racial makeup of the city was 95.3% White, 0.8% Black or African American, 0.5% Asian, 0.5% from other races, and 2.8% from two or more races. Ethnically, the population was 1.4% Hispanic or Latino of any race.

As of the census of 2010, there were 3,868 people, 1,659 households, and 1,037 families living in the city. The population density was 1,272.4 inhabitants per square mile (491.3/km). There were 1,805 housing units at an average density of 593.8 per square mile (229.3/km). The racial makeup of the city was 98.3% White, 0.5% African American, 0.2% Native American, 0.5% Asian, 0.3% from other races, and 0.3% from two or more races. Hispanic or Latino of any race were 0.8% of the population.

There were 1,659 households, of which 28.3% had children under the age of 18 living with them, 49.1% were married couples living together, 9.3% had a female householder with no husband present, 4.0% had a male householder with no wife present, and 37.5% were non-families. 32.4% of all households were made up of individuals, and 16.6% had someone living alone who was 65 years of age or older. The average household size was 2.27 and the average family size was 2.87.

The median age in the city was 41.2 years. 23.6% of residents were under the age of 18; 7.4% were between the ages of 18 and 24; 23.1% were from 25 to 44; 26.1% were from 45 to 64; and 19.8% were 65 years of age or older. The gender makeup of the city was 47.4% male and 52.6% female.

As of the census of 2000, there were 4,070 people, 1,706 households, and 1,079 families living in the city. The population density was 1,441.1 people per square mile (557.2/km). There were 1,799 housing units at an average density of 637.0 per square mile (246.3/km). The racial makeup of the city was 99.24% White, 0.07% African American, 0.29% Asian, 0.10% from other races, and 0.29% from two or more races. Hispanic or Latino of any race were 0.42% of the population.

There were 1,706 households, out of which 28.3% had children under the age of 18 living with them, 52.8% were married couples living together, 8.0% had a female householder with no husband present, and 36.7% were non-families. 31.8% of all households were made up of individuals, and 18.1% had someone living alone who was 65 years of age or older. The average household size was 2.31 and the average family size was 2.93.

In the city, the population was spread out, with 23.5% under the age of 18, 9.0% from 18 to 24, 25.1% from 25 to 44, 21.9% from 45 to 64, and 20.5% who were 65 years of age or older. The median age was 40 years. For every 100 females, there were 89.3 males. For every 100 females age 18 and over, there were 87.0 males.

The median income for a household in the city was $32,723, and the median income for a family was $47,500. Males had a median income of $30,683 versus $22,331 for females. The per capita income for the city was $17,797. About 6.4% of families and 8.9% of the population were below the poverty line, including 8.9% of those under age 18 and 9.7% of those age 65 or over.

Lancaster Municipal Airport (73C) serves the city and surrounding communities.

• U.S. Route 61 ("Madison Street"), passes north–south through the center of the city.
• Highway 35 enters east on (“ South Harrison Street and Cherry Street”), then follows Us 61 (“Madison Street”)
• Highway 29, bypasses the city to the east.
• County Trunk Highway A, passes east–west through the center of the city.

Until 1980, the village was served by a Chicago and North Western branch line from Madison The village was the end of the branch line.

Lancaster Community School District is the public school district for the community. The town also has a Catholic school.

Lancaster calls itself "The City of the Dome" after the octagonal glass and copper-clad dome of its courthouse, which was designed by Armand Koch and built in 1905. In the spandrels of the courthouse dome are four allegorical murals painted by Franz Edward Rohrbeck.

The Municipal Building (1922) is an example of Prairie School early modern architecture, which, like the courthouse, has been placed on the National Register of Historic Places.

The L. J. Arthur House, noted for its architecture, is also listed on the National Register.

The Lancaster Post Office contains a Depression-era mural, painted under the Works Progress Administration program in 1940.

The stone and wood Patrick and Margaret Kinney House in Lancaster was designed by Frank Lloyd Wright, one of 45 Wright structures in Wisconsin.

• List of cities in Wisconsin

• Official website
• Sanborn fire insurance maps: 1894 1899 1905 1912