The Des Plaines crater is a buried impact structure beneath eastern Des Plaines, Illinois, under part of the Chicago area. Nothing is visible at the surface, but underground evidence shows a crater about 5.5 miles wide and covering roughly 25 square miles, concealed beneath 75 to 200 feet of glacial till. Its age remains uncertain, with estimates ranging from about 280 million to 2 million years old. Well logs, seismic surveys, tilted and broken rock layers, and faulting with up to 600 feet of vertical displacement reveal the structure. First noticed in 1893, it was later recognized as an impact crater based on its uplifted center and shatter cones.