1631 Kopff (provisional designation 1936 UC) is a stony Florian asteroid from the inner regions of the asteroid belt, approximately 9 kilometers in diameter. It was discovered on 11 October 1936, by Finnish astronomer Yrjö Väisälä at Turku Observatory in Southwest Finland.^{[9][lower-alpha 1]} It was later named after German astronomer August Kopff.^[2]

Kopff is a member of the Flora family, one of the largest collisional families of stony S-type asteroid. It orbits the Sun in the inner main-belt at a distance of 1.8–2.7 AU once every 3 years and 4 months (1,220 days). Its orbit has an eccentricity of 0.21 and an inclination of 7° with respect to the ecliptic.^[1] First identified as 1926 TH at Heidelberg in 1926, the body's observation arc begins with its official discovery observation at Turku in 1936.^[9]

This minor planet was named for German astronomer August Kopff (1882–1960). He was first an assistant to Max Wolf, and became later a prolific discoverer of minor planets himself. In 1924, Kopff became Director of the Astronomisches Rechen-Institut in Berlin, and, after the western section moved to Heidelberg, he also became director of the Heidelberg Observatory. Under his leadership, the third Catalogue of Fundamental Stars (FK3) was compiled and the work on the fourth catalogue (FK4) was initiated. The lunar crater Kopff is also named in his honour.^[2] The official naming citation was published by the Minor Planet Center on 20 February 1976 (M.P.C. 3931).^[10]