"We ended up with a high concentration of millionaires and multimillionaires, and they predominantly located on the east side of Seattle, " says Mr. Deely, citing tech titans like Bill Gates and Paul Allen.

WSJ: Luxury Real Estate's Ritziest Gold Coast

The eastern suburbs have been home to many of Seattle's wealthy residents since the late 1800s, but the software boom in the 1990s sparked new interest in Medina, Bellevue and Mercer Island, says John Deely, principal managing broker at Coldwell Banker Bain based in Seattle.

WSJ: Luxury Real Estate's Ritziest Gold Coast