Camped here on July 4th weekend after originally aiming to camp at North Fork campground about a half mile down the road. We arrived late on July 3rd at North Fork and all of the walk-in sites were taken and the campground was slammed. Just up the road Onion Valley's sites (all walk-in / first come, first served) were wide open. A few people came late on the 4th, but still was pretty quiet. The swimming hole that draws the crowds to North Fork is easily accessible from Onion Valley. Fill up your water at the running spring fountain there too as there's no running water at Onion Valley. There are vault toilets, fire rings, and picnic tables though. Great spot overall.