Browse Items (1 total) Tags: Old Mill Dam Browse All Browse by Tag Search Items Sort by: Title Creator Date Added Photographs of Rock Springs Photographs of Rock Spring and of old mill dam. Tags: 1908, dam, Decatur IL, lake, Lake Decatur, Old Mill Dam, Photo File: Lake Decatur, Rock Springs, Sangamon, Sangamon River Featured Item Financial Report - May 1, 1970-January 31, 1971 This is the financial report for May 1, 1970-January 31, 1971.