| State: | SD |
| Type: | SD |
| Route: | 240 |
| Section: | 216 |
| Alternate Name: | Badlands Loop |
| Length Mi: | 40.033 |
| Length Ref: | [1] |
| Direction A: | West |
| Terminus A: | in Wall |
| Junction: | in Badlands National Park northeast of Interior |
| Direction B: | East |
| Terminus B: | south of Cottonwood |
| Counties: | Pennington, Jackson |
| Previous Type: | SD |
| Previous Route: | 239 |
| Next Type: | SD |
| Next Route: | 244 |
South Dakota Highway 240 (SD 240), also signed as the Badlands Loop, is a 40.033adj=midNaNadj=mid state highway in southeastern Pennington and northwestern Jackson counties in South Dakota, United States, that travels through the eastern portion of Badlands National Park.
SD 240 begins in Wall at exit 110 of Interstate 90 (I-90). 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. Because the highway enters a national park, there is an entrance fee charged along the highway at either entrance to the park. The fee is $30 per passenger vehicle, good for 7 days.
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. Construction began in the early 1930s. By 1944, a gravel surface was on the Badlands Loop alignment, and by the late 1940s, the Badlands Loop was signed as U.S. Route 16 Alternate (US 16 Alt.), in addition to SD 40 along the eastern portion of the loop. These two numbers were used until the early 1970s, when the SD 40 number was replaced by an extension of SD 44 (which entered the park from the southeast rather than the northeast).
Around 1980, US 16, which traveled concurrently with I-90, was truncated at its eastern end to Rapid City. Since US 16 Alt. no longer met the parent route, the route number was changed to SD 240.