Union or Union City is a small census-designated place in Mason County, Washington, United States. The community lies along the southern shore of the Great Bend of the Hood Canal, near the mouth of the Skokomish River, which flows from the nearby Olympic Mountains. The U.S. Census reported a population of 631 inhabitants in the 2010 census. The ZIP …Union or Union City is a small census-designated place in Mason County, Washington, United States. The community lies along the southern shore of the Great Bend of the Hood Canal, near the mouth of the Skokomish River, which flows from the nearby Olympic Mountains. The U.S. Census reported a population of 631 inhabitants in the 2010 census. The ZIP Code for Union is 98592.