MN is the postal abbreviation for Minnesota. The other official United States Postal Service abbreviations for states that begin with M are MS for Mississippi, MO for Missouri, MT for Montana, ME for Maine, MD for Maryland, MA for Massachusetts and MI for Michigan.
The United States Postal Service released these official abbreviations in October 1963. Prior to 1963, the Postal Service preferred the full state name spelled out on parcels and letters. They tolerated abbreviations and developed preferred abbreviation lists in 1831, 1874 and 1943. With the adoption of zip codes in June 1963 came a new list of two to four letters. The list was ultimately pared down for the list that stands today.