Putnam Valley is a town in Putnam County, New York, United States. The population was 11,809 at the 2010 census. Its location is northeast of New York City, in the southwestern part of Putnam County.…Putnam Valley is a town in Putnam County, New York, United States. The population was 11,809 at the 2010 census. Its location is northeast of New York City, in the southwestern part of Putnam County.Putnam Valley calls itself the "Town of Lakes".