U.S. Federal Route 40 runs east-west across Central Guernsey County. From the Muskingum/Guernsey County Line to Old Washington, this runs along the Interstate 70 corridor. From Old Washington to the Guernsey/Belmont County Line this run with I-70. U.S. Rt. 40 passes through the following towns in Guernsey County. Cassell Cambridge Old Washington U.S. Rt. 40 is multi-plexed in Guernsey County. U.S. Rt. 22, from the Muskingum/Guernsey County Line to Cambridge. Ohio State Route 285, at Old Washington. Interstate 70, from Old Washington to the Guernsey/Belmont County Line.