Monday, October 22nd is the last day for South Dakota residents to be able to register to vote in the upcoming November election.
You can either log on to the Secretary of State's website and download and fill out the form and bring it in to your county auditor or you can simply go to their office and they will help you through the process. Just be sure to bring in your driver's license.
People living in Iowa or Minnesota can register and vote on election day, so this is only applies to South Dakota voters.