California State Route 242

State Route 242 (SR 242) is an approximately 3.4-mile (5.5 km) state highway in Contra Costa County, California that links Interstate 680 at the Pleasant Hill–Concord border to State Route 4 in Concord. 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–San Joaquin River Delta region.

In 2000, State Route 242 was widened to six through-traffic lanes for the entire route. Ramp metering is present at all onramps, and is used southbound in the morning and northbound in the evening. It was signed as part of State Route 24 until ca. 1987.