Formed in the summer of 2018, the Rum River Mallards joined the USPHL as a member of the Midwest-West Division. Team president Glen Lucken and long-time hockey coach Brad Zangs led the Mallards as its first head coach and GM. A group of investors, including Zangs, purchased the Ironwood Fighting Yoopers who were established in 2014 competing in the Minnesota Junior Hockey League one season before joining the USPHL (2016–18).
Season one ended with a fifth-place finish in the nine-team Midwest-West Division. Rum River earned their first-ever victory on September 28, 2018 defeating the host Hudson Havoc 6–4.
After 17 games played the team was sold to local businessman Eddy Wilkinson who hired new head coach, Jimmy Jensen.
The first Mallards season ended with 51 points, just one point back of the Minnesota Blue Ox, despite two regular season games being cancelled. Unable to reschedule those games before the playoffs the Blue Ox hosted the best-of three series as the higher seed. On September 28, 2018 the Mallards defeated the Blue Ox 11-6 before being eliminated the following night in Game 3.
After a good start to their second season Jimmy Jensen stepped away from the bench for family reasons. He was replaced in early December by Triston Jensen (no relation), a former goaltender who played in both the MNJHL and USPHL.Triston play collegiate hockey at the ACHA level at Saginaw Valley State University.
Rum River ended the 2019–20 season as the fifth seed with another playoff matchup against the Blue Ox. After winning Game 1 the Minnesota Blue Ox responded by winning Games 2 and 3 to advance in the division playoffs.