Detroit is the most populous city in the U.S. state of Michigan, the largest city on the United States–Canada border, and the seat of Wayne County. The municipality of Detroit had a 2016 estimated population of 672,795, making it the 23rd-most populous city in the United States. The metropolitan area, known as Metro Detroit, is home to 4.3 million people, making it the second-largest in the Midwest after Chicago.Detroit is a major port on the Detroit River, one of the four major straits that connect the Great Lakes system to the Saint Lawrence Seaway. The Detroit Metropolitan Airport is among the most important hubs in the United States. The City of Detroit anchors the third-largest economic region in the Midwest, behind Chicago and Minneapolis, and the 14th-largest in the United States. Detroit and its neighboring Canadian city Windsor are connected through a tunnel and the Ambassador Bridge, the busiest international crossing in North America.