The grove of black jack trees that gave this town its original name stood near an Indian camping ground atop the highest point in present Hopkins County, and an Indian trail crossing the grove later became a major wagon freighting route. Black Jack Grove Post Office opened in 1848 in the home of John W. Matthews, the first postmaster. In 1851 D. W. Cole bought a tract including the grove from Elizabeth Wren and began selling town lots; he also operated a store and donated land for the first Masonic Lodge building, while Henry Bingham ran a tavern that also served as a hotel. By 1860, Black Jack Grove was a thriving settlement with several stores, two physicians, two blacksmiths, other tradesmen, and a school in a log structure; later, a vacant store served as a school and church facility. To avoid confusion with another Black Jack Post Office, the town was renamed in 1896 for legislator and Confederate veteran Robert H. Cumby. After 1900, two banks opened and the town incorporated, but later its population declined as improved highways reduced Cumby's importance as a trading center. One of its best-known citizens was noted author Ben K. Green (1912-1974).