Most of South Dakota operates on Central Standard Time (CST) during winter months, which is 6 hours behind Coordinated Universal Time (UTC-6). During daylight saving time, observed from the second Sunday in March to the first Sunday in November, South Dakota switches to Central Daylight Time (CDT), which is UTC-5.
The majority of South Dakota follows Central Time, including Sioux Falls and Watertown. However, western counties including Rapid City observe Mountain Time (UTC-7/UTC-6). The timezone boundary roughly follows the Missouri River.
South Dakota spans two time zones. When it's 9 AM in Sioux Falls (Central Time), it's 8 AM in Rapid City (Mountain Time). Businesses coordinating across the state must account for this one-hour difference.