There are 19 US Post Offices in Hudson County serving a total of 867,132 residents equating to 45,639 residents per post office. It's estimated that approximately 1,384,039 packages are handled across the 19 county post offices annually. Hudson County, a county in the U.S. state of New Jersey, lies west of the lower Hudson River, which was named for Henry Hudson, the sea captain who explored the area in 1609. Part of New Jersey's Gateway Region in the New York metropolitan area, Jersey City is its largest city and county seat. As of 2015, Hudson County was the fastest growing county in New Jersey compared to 2010, with a Census-estimated population in 2015 of 674,836, an increase of 6.4% from the 2010 United States Census, when its population was enumerated at 634,266, in turn an increase of 25,291 (+4.2%) from the 608,975 enumerated in the 2000 Census. Hudson County is the fourth-most populous county in the state. Hudson County is the geographically smallest and most densely populated county in New Jersey and the sixth-most densely populated county in the United States, with 13,731.4 residents per square mile of total area in 2010."