Mill River, MassOld Paper Mill Published By: W. R. Field's Series Postmarked: Mill River, Mass, Sept 27, 1911. The is a very old black and white postcard view of the old Paper Mill, in Mill River, Mass. This town is very popular and it sits near Hartsville and New Marlboro. I am not sure w in town the paper mill was, but you can be sure that by now all traces of it are long gone. Please email me any questions or comments. I thank you for taking the time to look through all my auctions. John Keller. Be sure to add me to your favorites list !