Very close to southwest entrance
Right inside the Lassen Volcanic Park, just to the right after entering is the campground. It was $14 per night and was the only campground in the park that had spots available at the time. Tables and fire pits, close to the parking lot. Nice bathrooms, as well as a dish washing area in the back of the bathroom building, which was really nice. Sites were walk in/hike in only, but because the parking was relatively close, it was easy. Very close the the visitor center.