Fond du Lac is a city in Fond du Lac County, Wisconsin, United States. The population was 43,021 at the 2010 census. The city forms the core of the United States Census Bureau's Fond du Lac Metropolitan Statistical Area, which includes all of Fond du Lac County . Fond du Lac is the 342nd largest Metropolitan Statistical Area in the United States. The Fond du Lac MSA and the Beaver Dam , Wisconsin Micropolitan Statistical Area, form the larger Fond du Lac-Beaver Dam Combined Statistical Area.