The Pioneer Baseball League began in 1939 with six teams in Idaho and Utah. The league suspended operations for the 1943 through 1945 seasons. In 1948, the league expanded into Montana. At that time, several of the teams were operating as minor league affiliates of Pacific Coast League teams, which were unsuccessfully trying to grow into a major league. When the Los Angeles Dodgers displaced the Hollywood Stars] PCL team, they moved to Salt Lake City, Utah, taking away the Pioneer League's largest market. By 1959, the league was down to six teams, and by 1964, there were only four, but by the end of the 1970s there were eight teams.
The league is divided into a Northern Division and a Southern Division.
Current member teams: