There are 28 US Post Offices in Union County serving a total of 648,652 residents equating to 23,166 residents per post office. It's estimated that approximately 1,035,321 packages are handled across the 28 county post offices annually. Union County is a county in the U.S. state of New Jersey. According to 2015 U.S. Census estimates, its population was 555,786, an increase of 3.6% from the 2010 United States Census, when its population was enumerated at 536,499, in turn an increase of 13,958 (2.7%) from the 522,541 enumerated in the 2000 Census and making Union County the seventh-most populous county in the state, having been surpassed by Ocean County. Union County is part of the New York metropolitan area. Its county seat is Elizabeth. The Bureau of Economic Analysis ranked the county as having the 119th-highest per capita income of all 3,113 counties in the United States (and the eighth-highest in New Jersey) in 2009. A study by Forbes.com determined that Union County pays the second-highest property taxes of all U.S. counties, based on 2007 data. With a population density of 4,955 people per square mile (water excluded), Union County was the 15th-most densely populated county in America as of the 2010 Census, and third-densest in New Jersey, behind Hudson County (ranked 6th at 9,754) and Essex County (ranked 11th at 6,126). Union County was formed on March 19, 1857, from portions of Essex County; it was the last of New Jersey's 21 counties to be established."