How I wish we were still there - I lived not far from where you are.
There are lots of things to do with the horses, it's just a matter of finding them. Becoming involved with groups such as the 4-H (if you are too old to do so as a member, they are always looking for adult help/leaders/volunteers), the posse (we were in Yamhill County, so I can't guarantee there is one for your county - but I could send you the name/number of someone who could tell you - he was on the posse where we were at), etc is a great way to start building a network of horse people and activities. The county fairs will have a lot of horse related stuff and, again, be a great way to meet people who share your love of horses.....advantage over the state fair is that a) they are smaller (more friendly) and b) there are more of them as you can reach several counties from where you are vs. just one state fair.
I would suggest stopping by the local WILCO farm store (personal preference here for the Newberg or McMinnville locations, lol.....I worked for both over a 4 year period) -- most of the staff will be all too happy to "talk horse" with you and that's a great way to build that horse network and get the inside scoop on events, clubs, etc.
The area you are in is actually very big for horses - whether it's the backyard pony or two to large scale operations......it's just a matter of getting your foot in the door, so to speak, so you can be a part of it all.