Winnebago is an unincorporated community in the Town of Oshkosh in Winnebago County, Wisconsin, United States. It is located just outside the northeast edge of the city of Oshkosh. The Winnebago Mental Health Institute is located in Winnebago. The ZIP code is: 54985. U.S. Route 45 ran through the community until the road's route was moved west; the former route is now occupied by County Highway A.