Hi Alcia: I have not sought out or joined any specific groups, but I can tell you what ended up working for me. My daughter is now 3 and I left my career to become a SAHM not too long after she was born...the change is pretty substantial. ;) One place that I found a good network of moms to talk to was through my daughters "pre-school" -- it was a Twos program where the moms were participants in the 1 day a week (2 hours) pre-school type program. There was a timeslot allocated there for moms to step out into a separate room and talk about relevant topics or whatever we wanted and there was a teacher in the room with us leading or at least participating in the discussions. That helped since all the moms had at least one kid the same age/stage. I am sure there are many such programs in the Hillsboro area. This particular school was A Child's Way in Cedar Mill (near the library).
You will likely also find moms at library programs and activities like Gymboree. I found a great group of moms to talk to at the Cedar Hills Gymboree through the Art Class (ask for teacher Cindy's sessions if you decide to try this). Another activity where I made some great mom friends and had a chance to literally do locker-room talks is at Children of the Sea (swim school) by Wash Sq Mall. I started my daughter there at 7 months. Great program and a great chance to get to know some moms and chat it up.
And then finally, there are blogs like this one that work pretty well - you get a wide variety of perspectives and that helps find what works for you and your family. But if you are looking to make friends with other moms too, then the classes/programs are the best way in my opinion.
Hope these ideas help!