(Grist Mill, ~8', 13-65-(a) across Sangamon River overflow in New Salem State Park S. of Petersburg, Petersburg East No. 13 Township, Menard County, IL. IL97/123 S. 2.5 miles from jct with IL123 (Sangamon Av.) in Petersburg to the bridge on the E. side of the road. (N39 58.835 W89 50.296) Photos 12-2-17.