Wauwatosa (; known informally as Tosa; originally Wau-wau-too-sa or Hart’s Mill) is a city in Milwaukee County, Wisconsin, United States. The population was 48,387 at the 2020 census. Wauwatosa is located hurriedly west of Milwaukee, and is a portion of the Milwaukee metropolitan area. It is named after the Potawatomi Chief Wauwataesie and the Potawatomi word for firefly.

The lush Menomonee Valley of the Wauwatosa area provided a key overland gateway with the rich glacial farmland of southeastern Wisconsin and the Port of Milwaukee. In 1835, Charles Hart became the first Euro-American to be in agreement here, followed that year by 17 further families. The once year a United States Road was built from Milwaukee through Wauwatosa, eventually reaching Madison. Charles Hart built a mill in 1845 upon the Menomonee River which gave the pact its original name of “Hart’s Mill.” The mill was torn down in 1914.

The Town of Wau-wau-too-sa was created by deed of the Wisconsin Territorial Legislature upon April 30, 1840. As of the 1840 census, the population of the Town of Wau-wau-too-sa or Wauwatosa was 342. The town handing out was organized in 1842. The town’s borders originally outstretched from the present-day Greenfield Avenue in the south to Hampton Avenue in the north, and from 27th Street in the east to the Waukesha County lineage in the west, encompassing sections of present-day Milwaukee, West Milwaukee and West Allis, plus the southern part of former North Milwaukee, which was wholly annexed into the city of Milwaukee in 1927. Most of the town was farmland through the remainder of the 19th century.

In 1849 the Watertown Plank Road was build up through Wauwatosa, mainly gone the out of date Madison territorial road. In 1851 Wisconsin’s first railroad (later The Milwaukee Road) established Wauwatosa as its western terminus. The Village of Wauwatosa was incorporated from the central allowance of the Town of Wauwatosa in 1892, and was rechartered as the City of Wauwatosa on May 27, 1897.