The league got its start when American investors made a deal with the Thunder Bay Junior A Hockey League, changing the league's name to the Thunder Bay-Minnesota League in 1971-72 and admitting a single American team. In 1972, the league changed its name to the Can-AM Junior Hockey League, which still ran under the jurisdiction of the Canadian Amateur Hockey Association.
In 1973, the core of the teams broke away from the CAHA and started a new league called the Midwest Junior Hockey League. It would feature all American teams, except for the first year where it still had the CAHA-affiliated Thunder Bay Hurricanes.
By the late 1970s, the league merged with the United States Hockey League. This move turned the USHL from a Semi-Professional league to what would be USA Hockey's premier Junior hockey league within a handful of years.