Local jurisdictions may have ordinances restricting the number and size of signs. If a jurisdiction does have such ordinances, in an even year these ordinances cannot be enforced for a specified time before and after election day. (Minnesota Statutes 211B.045). In jurisdictions which have no sign ordinance, campaign signs may be posted in any size and number throughout the year.
For 2018, the period when local sign ordinances may not be enforced begins June 29 and ends November 16.
The Minnesota Department of Transportation's webpage contains information about signs along highway right of way.