State Route 242 (SR 242) is a short three-mile (5 km) connector route that links Interstate 680 north of Pleasant Hill to State Route 4 in Concord. In 2000, State Route 242 was widended to six through-traffic lanes for the entire route. Ramp metering is present at all onramps, but is not used at this time. It was signed as part of State Route 24 until ca. 1987. Currently, along with Interstate 580, State Route 24, Interstate 680, and State Route 4, it serves as the most direct route between the San Francisco Bay Area and the Sacramento River Delta region of Northern California.

SR 242 is part of the California Freeway and Expressway System. The route begins as a freeway at Interstate 680 in Concord. It then heads north, meeting Clayton Road, Concord Avenue, Grant Street, and Olivera Road before meeting its north end at State Route 4 just west of the former Concord Naval Weapons Station.

Except where prefixed with a letter, postmiles were measured on the road as it was in 1964, and do not necessarily reflect current mileage. The entire route is in Concord, Contra Costa County.