National Parks: http://en.wikipedia.org/wiki/National_park

State Parks: http://en.wikipedia.org/wiki/State_park

Urban Parks: http://en.wikipedia.org/wiki/Urban_park

Private Parks: http://en.wikipedia.org/wiki/Park#Private_parks

National Recreation & Parks Association: NRPA is the leading advocacy organization dedicated to the advancement of public parks and recreation opportunities. Founded in 1965 through the merger of 5 national organizations dedicated to the same cause, NRPA has grown over the years - in total membership, in outreach efforts, in building partnerships, and in serving as the voice and defender of parks and recreation. http://www.nrpa.org/

City of Portland, OR Parks & Recreation Department: http://www.portlandonline.com/parks/