Mound 12 is illustrated on the Patrick Map as a small, conical mound west of both Mound 11 and Sand Prairie Lane. Unfortunately, this mound does not appear as a distinct contour on the 1966 UWM Map. Consequently, there is little data on Mound 12 except Patrick's suggestion of its conical shape and the appearance in that area of a small, oval rise on the UWM Map. Mound 12 is reported by Moorehead (1923: 45, 1925: 98). His comments were summarized in Titterington (1938: 7):
There is a small mound about 1/4 of a mile north of Monks Mound from which a large number of unfinished celts were taken about 30 or 40 years ago. All were pecked out into a fairly good shape except for some on which the bit had not been formed. The largest weighed about 25 pounds.