Held each July at the Enumclaw Expo Center, the King County Fair is one of the last county fairs in Washington that still feels genuinely agricultural rather than suburban. Livestock judging, rodeo events, 4-H competitions, and the usual carnival sprawl attract families from across the region. The fair has been running for well over a century and retains a character that distinguishes it from the corporate state fair in Puyallup.
The rodeo in particular is worth attending if you're in the area in July — barrel racing, bull riding, and team roping with serious competitors. The fairgrounds are also used for other events through the summer; check the Expo Center calendar.