The Florence Mill, known later as the U.S. Envelope Building after being absorbed by the U.S. Envelope Company, is a former industrial facility located at 121 West Main Street in the Rockville section of Vernon, Connecticut. It is a four story brick structure, more than 200 feet (61 m) in length, with a Second Empire-style mansard roof and an Italianate tower. It was built in 1864 to replace an earlier textile mill which was destroyed by fire. In 1881, it was described as the largest brick building in Rockville. After purchase by White & Corbin, the building was expanded and became the largest manufacturing plant of its kind in the United States.