Brookfield is a city in Waukesha County, Wisconsin, United States. The population was 38,649 at the 2000 census. Its 2006 estimated population was 39,607. Brookfield is the second largest community in Waukesha County, and the leading commercial suburb of Milwaukee. Formed in the 1950s from the Town of Brookfield, which still survives, the City of Brookfield shares the Elmbrook School District with the Town and with Elm Grove, Wisconsin, although police and fire services are separate for Town and City.