Illinois State Route 78 is a north-south highway in Central Carroll County. It runs the Carroll/Whiteside County Line, near Fair Haven, to the Carroll/Jo Daviess County Line, near Pleasant Valley. IL St Rt 78 passes through the following towns in Carroll County. Ideal Mt. Carroll
IL St Rt 78 is not multi-plexed in Carroll County. IL St Rt 78 intersects the following highways in Carroll County. Illinois State Route 40, at Mt. Carroll.
A junction marker on WB U.S. Rt. 52/IL St Rt 64. NB IL St Rt 78 at U.S. Rt. 52/IL St Rt 64. SB IL St Rt 78 south of U.S. Rt. 52/IL St Rt 64. NB IL St Rt 78 north of Seminary St. in Mt Carroll. NB IL St Rt 78 at Turnbaugh St in Mt. Carroll. NB IL St Rt 78 at Market St in Mt. Carroll.
