Wisconsin State Route 78 is a north-south highway in Southeastern Sauk County. It runs from the Sauk/Columbia County Line, near Merrimac, to the Sauk/Dane County Line, near Sauk City. WI St Rt 78 passes through the following towns in Sauk County. Merrimac Prairie du Sac Sauk City WI Rt 78 is multi-plexed in Sauk County. Wisconsin State Route 113, near Merrimac. BUSN U.S. Rt. 12, from near Prairie du Sac to Sauk City. Wisconsin State Route 60, from near Prairie du Sac to Sauk City.