2010Flipped from DemocraticFinal resultsIncumbent defeated
2010 election for South Dakota Legislative District 12
South Dakota State Senate · South Dakota
Mark Johnston (R) won with 54.4% of the vote, defeating Sandy Jerstad (D) by 8.7 points, a seat Democrats won last time.
Mark JohnstonRepublican · winner
54.4%6,094
Sandy JerstadDemocrat · incumbent
45.6%5,117
11,211 votes
Source: Harvard Dataverse / Carl KlarnerUpdated Sep 30, 2026, 7:29 AM ET
The seat over time
D − R margin in this seat's races around 2010
Races before and after
Source: Harvard Dataverse / Carl KlarnerUpdated Sep 30, 2026, 7:29 AM ET