Indiana State Route 28 runs east-west across Central Clinton County. This connects Frankfort to Interstate 65. IN St Rt 28 passes through the following towns in Clinton County. Fickle Jefferson Frankfort IN St Rt 28 is multi-plexed in Clinton County. U.S. Rt. 421, from Franfort to near Boyleston. IN St Rt 28 intersects the following highways in Clinton County. Interstate 65, near Fickle. U.S. Rt. 421, at Frankfort. Indiana State Route 38, at Frankfort. Indiana State Route 39, at Frankfort. Indiana State Route 29, near Boyleston. U.S. Rt. 421, near Boyleston.