Pari-Mutual wagering was legalized in Oregon 1933, but it's roots go back to 1891 when horse racing became part of the fair at Tillamook. Over the years fair racing was in Salem, Gresham, Union and Grants Pass. In 1946 the states only non agricultural track was open in Portland.
Portland Meadows really lit up the horse racing world, when it debuted under the lights on September 14, 1946, allegedly the first thoroughbred track to do so.
To this date other than tracks at Salem and Gresham, all other tracks are still in business. Oregon is a non racino state, but Portland Meadows is trying to get instant racing approved.
It's hard to date something on the internet, because it lasts forever, but in 2017, Oregon Fairs raced from June to September. Five tracks most running three days starting on the eastern border in Union, traveling across the state till reaching the western border in Tillamook, before ending the season mid state in Burns.
I have put this out there, I messed up. After further research I realized that I missed two other Oregon Fairs, Burns and Prineville. I will catch up with them on the next go around, hopefully by next years races in 2014.
Well, obviously that didn't happen as it is now 2017. Being from the east coast my knowledge of racing in the Pacific Northwest is a little light, but lately I have been in contact with a gentleman named Ted Michelakos, who does have that knowledge. With his help and some material's he's provided, I should be able to add these tracks, as well as the Klamath County Fair which I had no idea existed.
In another update it looks like instant racing was implemented at Portland Meadows.