William John Janklow was an American lawyer and politician and member of the Republican Party who holds the record for the longest tenure as Governor of South Dakota: sixteen years in office. Janklow had the third-longest gubernatorial tenure in post-Constitutional U.S. history at 5,851 days.

The governor of South Dakota is the head of government of South Dakota. The governor is elected to a four-year term in even years when there is no presidential election. The current governor is Kristi Noem, a member of the Republican Party who took office on January 5, 2019.