 I-90 traverses the northern portion of Mercer Island and is then carried from the island to Bellevue over the East Channel of Lake Washington by the East Channel Bridge.Mercer Island is located closer to Bellevue than it is to Seattle, and is therefore often considered to be part of King County's Eastside.The population was 22,699 at the 2010 census and an estimated 25,894 in 2019.