Redwood National and State Parks offer four developed campgrounds, three in the redwood forest and one on the ocean. Tidbits to know: no trailer hook-ups exist; there is a charge for each extra vehicle per site; and day use fees are charged.
http://www.nps.gov/redw/planyourvisit/campgrounds.htm

I’ve hiked the Coastal Trail, Last Chance section, located at the end of Enderts Beach Road or at milepost 15.6 on Highway 101: 6 miles. It starts in Redwood National Park and enters Del Norte Redwoods State Park. It’s very beautiful. I went in May and didn’t see another person all day.

I also hiked the Boy Scout Tree Trail in Jedediah Smith Redwoods State Park and that was nice too. http://www.redwoodhikes.com/Jed%20Smith/Boy%20Scout.html

If you’re going up to Humboldt County, Check out Pamplin Grove, Richardson Grove, Humboldt Redwoods, are my favorits. But below is a great website for you to check out for camping in and around these areas. Good Luck!