The small Wynants Kill is known in the history of water power for Merritt et al. vs. Brinkerhoff et al. (1820) and for the Burden Water Wheel, largest in the world (1851)—events that bracket the first, intense, period of industrialization on the stream (a "portrait" of the climax is derived from data in the 1855 census of New York state). The mill sites were connected not only by geography and their feudal tenure, but also, vertically, by a cooperative association formed by the lessees of the water privileges (1829), by industrial arrangements, and by community development. We will use postal activity indices, generated from the Official Registers (a business data source not widely appreciated), for the measure and timing of this commercialization of the Wynants Kill watershed.