From KOA.com:

Get A Free Night Of Camping May 11-12! We’re taking reservations for KOA’s annual Come Camp & Care With Us Weekend Friday, May 11 and Saturday, May 12. This year, campers who stay at a participating KOA as a paying guest on Friday, May 11 will receive a FREE NIGHT of camping on Saturday, May 12. View the list of participating KOA Kampgrounds and make your reservation today!