Professional baseball was still in its infancy when the first minor league was officially established on this day in baseball in 1879. But that does with a caveat, as the recognition by the National League and American Association did not occur until 1883.
Middle America was the location for a new league that was formed and fielded in 1879 with four teams. Although the Northwestern League folded after that lone campaign (the usual issues were at fault, mainly financial), it may have been dead, but not buried.
Perhaps this was a litmus test and although it took a few years, the Northwestern League returned, doubled in size and was party to the National Agreement of 1883. The following season, four more teams were added, including the Milwaukee Brewers. The league paused on August 13 due to multiple teams disbanding and only four clubs remained when play resumed.
After sitting out the 1885 season, the league gave it yet another shot and lasted two years before being replaced by the Western Association in 1887.
