State Route 142 Begins in London and acts as a spur of US 42 serving West Jefferson, although its interchange with I-70 primarily provides Interstate access to West Jefferson and nearby Lake Darby rather than as a connection to US 42. Sometimes the road (Plain City-Georgesville Rd) from that interchange northward to Plain City is also incorrectly referred to as Route 142 by locals. This road is actually designated as Madison CR 7, although a small portion of the road is a part of SR 142 from US 40 to I-70.

Originally, the eastern terminus was at West Jefferson The route was extended to meet I-70 when it opened in 1971. According to West Jefferson locals, ODOT hadn't originally planned for the SR 142 extension or its interchange with I-70, and felt the town would be adequately served by SR 29. The citizens protested, and gained the support of the Battelle Memorial Institute, located on Plain City-Georgesville Rd between US 40 and the proposed I-70. As a result, ODOT added an interchange at Plain City-Georgesville Rd to their plans, and extended SR 142 past Battelle to that interchange.[citation needed]