Devil's Lake State Recreation Area is a park and campground on the west shore of Devil's Lake, within (but remarkably isolated from) Lincoln City, Oregon. There are 33 RV sites, 54 tent sites, and 10 yurts. A trail leads to a dock on the lake shore. Ocean beach access at the D River State Recreation Site is an easy ten minute walk, partially on a boardwalk constructed over a swampy wetland.
This campground is something of a best-kept secret, in a tourist town where motel rooms run $200/night. The campground as a whole is open year-round, but some sites are closed during the winter (and into June) because the campground too was built on the bog.
More at 100 Steps.