The annual "Sunsets and Crabs" event by the Teardroppers of Oregon and Washington has been held here for a several years, and it is an amazing event. Good people, awesome trailers, and a great location with plenty of room right on the ocean.
The Old Mill RV Park & Event Center is large, and mostly caters to RVs. That particular area is somewhat separate from the group event area and has rows and rows of RVs all lined up. I don't know if I'd ever want to stay there. But the area for events is wide open and perfect (I know some people have also had things like family reunions). You can drive right up near the edge and set yourself up with a great view. Picnic tables and nice restrooms are included.
Pros: Amazing location with lots of space and good facilities.
Cons: The RV park is all on top of each other and I don't think I'd want to stay over there.
The Old Mill RV Park feels much more like a trailer park than a costal campground, but they do allow tent camping. I wouldn't recommend it as a destination place to camp, but if everything at the coast is totally full this one will do in a pinch. It's perfectly fine for sleeping.
We used Old Mill as a jumping off point for Cape Lookout (because their campground was totally full) -- it's a 20 minute-ish drive away through rural farm land and gorgeous coast. It's also convenient for fishing and clamming in the Tilamook bay if you're bringing your own boat.
The Old Mill is right off of the 101 in Girabaldi--super convenient to the little downtown. The bathrooms are really far away from most sites. We drove when we went there.
There aren't exactly "sites" more of a really big field with picnic tables and markings. This did come in handy since we my friends had a boat trailer, and we were able to also park that in our "site".