Wyoming Highway 257 (WYO 257), also known as the Casper West Belt, is a state highway in Natrona County, Wyoming. The 7.3-mile (11.7 km) highway forms part of a bypass around Casper and Mills, connecting WYO 220 in the south to U.S. Route 20 (US 20) and US 26 in the north. The road itself continues east on an expressway carrying US 20 and US 26 to a junction with Interstate 25 (I-25).

Natrona County is a county in the U.S. state of Wyoming. As of the 2020 United States Census, the population was 79,955, making it the second-most populous county in Wyoming. Its county seat is Casper.