There are 27 US Post Offices in Essex County serving a total of 37,233 residents equating to 1,379 residents per post office. It's estimated that approximately 59,428 packages are handled across the 27 county post offices annually. Essex County is a county located in the state of New York, in the United States. As of the 2010 census, the population was 39,370. Its county seat is the hamlet of Elizabethtown. Its name is from the English county of Essex. Along with Hamilton County, Essex is entirely within the Adirondack Park.