Emerald Mound and Village Site in Illinois preserves the remains of a Middle Mississippian village that operated as a satellite of Cahokia, the major regional center across the Mississippi River floodplain. The site contains traces of a village and five mounds, though modern activity destroyed two of them. Its largest earthwork is a two-tiered mound about 50 feet high, with a square base roughly 300 feet across and an upper tier about 150 feet across. Once regarded as the second-largest known mound in Illinois after Monks Mound, Emerald is important for showing how Cahokia's influence extended into surrounding communities.