Fenton is a city in the U.S. state of Michigan that lies mostly in Genesee County, but with small portions in Livingston County, and Oakland County. As of the 2000 census, the city population was 10,582. The city was incorporated from Fenton Township in Genesee County, but the city and township are administratively autonomous. In 2004, the city annexed a small portion of Holly Township in Oakland County.