As of the 2010 census, the population of Grays Harbor was 72,797. The county seat is Montesano and its largest city is Aberdeen. The county is named after a large estuarine bay near its southwestern corner. On May 7, 1792, Boston fur trader Robert Gray crossed the bar into the bay he called Bullfinch Harbor, but which later cartographers would label Chehalis Bay, and then Grays Harbor.