Minor League (1884)

Add to these the players of the various minor leagues and State associations, and it will be found that an aggregate of over 1,200 professional players were in the baseball arena during 1884.The Salt Lake Herald, December 21, 1884, p8

Previous earliest use (Dickson Baseball Dictionary, 3rd edition, 2009):
1ST USE. 1887 (Reach’s Official American Association Base Ball Guide; David Ball).