The 18th Senate District of Wisconsin is one of 33 districts in the Wisconsin State Senate. Located in east-central Wisconsin, the district comprises most of Fond du Lac County and the southern half of Winnebago County, as well as the city of Waupun, which crosses into northern Dodge County. The district also includes the cities of Fond du Lac and Oshkosh, and covers the south and west shores of Lake Winnebago.