From the Cascade Bicycle Club website:

31st Group Health Seattle to Portland Bicycle Classic
Saturday July 17, 2010 to Sunday July 18, 2010

“Welcome to the 31st Group Health Seattle to Portland Bicycle Classic official web site. This 200-mile bicycle ride is the largest multi-day bicycle event in the Northwest, with up to 10,000 participants riding from Seattle to Portland in one or two days. The route takes you through the scenic valleys, forests, and farmlands of western Washington and Oregon. Come join what Bicycling Magazine has listed as one of the best cycling events in the nation!

This event is now SOLD OUT!

Who rode in 2009?
9,999 other riders
Oldest rider: 87
Youngest rider: 2 years 4 months old
18% first-time riders
100 safety and medical riders
310 riders who have participated in 10+ STPs
Two riders who have ridden them all: Jerry Baker and Paul Wantzelius! In 2009, riders came from 46 states plus Australia, Bermuda, Canada, England, Puerto Rico, and Sweden.”

The Olympian says:
“Look out for STP cyclists this weekend”