 The route then enters the greater Oshkosh area and junctions with US 41 along Omro Road.WIS 21 continues along Omro Road, Oshkosh Avenue and Congress Avenue, ending at US 45 (Algoma Boulevard) on the northwest side of Oshkosh after crossing the upper Fox River east of Lake Butte des Morts.The route was first written into law in from La Crosse to Oshkosh.