The Florence Mill, known later as the U. S. Envelope Building, is a former industrial facility located at 121 West Main Street in the Rockville section of Vernon, Connecticut. Developed in stages between 1864 and 1916, it exhibits changes in mill construction technology over that period, include a rare early example of Second Empire architecture. Now converted into senior housing, it was listed on the National Register of Historic Places in 1978. In 1881, it was described as the largest brick building in Rockville, and continued in the production of textiles. It was purchased in 1881 by White & Corbin, who expanded the building several times, making it the largest manufacturing plant in the United States for the manufacture of envelopes. The building was used for this purpose by White & Corbin and its successors (including the U. S. Envelope Company), until 1975.