Old Mill, historically known as the Main College Building, is the oldest campus building of the University of Vermont. The first Main College was built in 1801 and 1802 by John Johnson, but it burned down in 1824. Johnson also designed its replacement.
The cornerstone for North College was laid on April 26, 1825 by Vermont Governor Cornelius P. Van Ness. Two months later, on June 29, General Lafayette laid the cornerstone for South College during his tour. A third building, Middle College, was added in 1829.
Each of the buildings was built 7 to 8 feet apart to keep a fire from destroying the whole thing again. They were connected in 1846. The building was added to the National Register of Historic Places in 1975, as part of the University Green Historic District.