According to Kare 11 TV: Coldest March temperature ever recorded in Minnesota: -35 F; Wikipedia disagrees

From kare11.com | Twin Cities, MN

...we broke a statewide record for March, Embarrass and Babbit both recorded -35 degrees on Thursday morning and that broke a statewide record for cold that held since 1896. International Falls(-28) and St. Cloud(-15) were a couple of spots that broke daily records for their specific location as well.

List of Minnesota weather records - Wikipedia, the free encyclopedia

Lowest Temperature −50 °F (−46 °C) March 2, 1897 Pokegama Dam