South Dakota Highway 42 (SD 42) is a segmented state highway in southeastern South Dakota, United States. The first segment is a six-mile-long (9.7 km) highway in Aurora County. The second and longest is 60 miles (97 km) long and connects Ethan and Sioux Falls. The final segment connects Sioux Falls to Iowa Highway 9 southeast of Rowena.

Aurora County is a county in the U.S. state of South Dakota. As of the 2020 census, the population was 2,747. The county was created in 1879, and was organized in 1881.