William Herschel discovered NGC 3931 = H III-769 on 12 Apr 1789 (sweep 919) and noted "cF, S." There is nothing at his position, but 1 min of RA preceding, and 2' north is UGC 6825. Philip Keenan rediscovered this galaxy on a Yerkes Observatory plate and labeled it NGC 3917A (assuming it was new) in his 1935 paper "Studies of Extra-Galactic Nebulae, Part I: Determination of Magnitudes" (ApJ, 82, 62). All objects were assigned NGC + letter designations based on the nearest NGC object on the plate. " He determined a magnitude of 13.9.

Karl Reinmuth, in his 1926 photographic survey, identified PGC 37168 as NGC 3931. This galaxy is close to WH's position, but UGC 6825 is much brighter and more likely to have been picked up. CGCG and MCG do not label their corresponding catalogue entries as NGC 3931. Both Harold Corwin and Malcolm Thompson discuss this identification.

400/500mm - 17.5" (3/19/88): fairly faint, small, round, bright core. Located 4.9' W of mag 8.6 SAO 28166. NGC 3917 lies 11' NNE. NGC 3931 is a member of the NGC 3992 (M109) group = LGG 258.

Notes by Steve Gottlieb