South Dakota Highway 240 (SD 240), also signed as the Badlands Loop, is a 40.033-mile-long (64.427 km) state highway in southeastern Pennington and northwestern Jackson counties in South Dakota, United States, that travels through the eastern portion of Badlands National Park.

It travels south to Badlands National Park, where it turns southeast.

At the Badlands Headquarters at Cedar Pass, the highway turns northeast, ending at exit 131 of I-90 near Cactus Flat.

[2] Eastern portions of the highway that are currently designated as SD 240 (generally from the park headquarters to Cactus Flat) were originally part of the original alignment of SD 40.

Around 1980, US 16, which traveled concurrently with I-90, was truncated at its eastern end to Rapid City.