SEATTLE — The very name of the Halcyon Mobile Home Park evokes happy tranquillity, and that’s what many residents were hoping it would be: an affordable place to enjoy their retirement in peace.

For a small fraction of what a standard house costs in the Pacific Northwest, a notoriously expensive corner of the country, they could own a cozy little home and lease the narrow sliver of ground beneath it for a few hundred dollars a month.

“All you had to worry about was paying your rent on time, and thinking about who you’d leave this shelter to after you were out of it,” said Eloise Micklesen, 74, a Halcyon resident. “But that changed last year, in July, when all of a sudden we were up for sale.”

The voracious Seattle real estate market, which had already wiped out almost every other mobile home park around, had finally come for Halcyon. A developer offered the owners $22 million, with plans to build 200 pricey townhomes on the 7.5-acre property near the city’s northern border.