1223 Neckar, provisional designation 1931 TG, is a stony asteroid from the outer region of the asteroid belt, about 26 kilometers in diameter. It was discovered by German astronomer Karl Reinmuth at Heidelberg Observatory in southern Germany on 6 October 1931. The minor planet was named after the 367-kilometre-long river Neckar, running through the southwestern parts of Germany and in particular through the city of Heidelberg, location of the discovering observatory. The river origins in the Black Forrest and flows into the Rhine river.