The Winfield festival itself is always the Thursday through Sunday that includes the 3rd Saturday in September. This year the dates are the 13th-16th. The campground opens Thursday a week earlier, this year the 6th. That week before the festival is its own event, with lots of great campground music before folks get distracted by the stage shows (it's also the time the most desirable camping spaces get taken). Their website is wvfest.com (stands for Walnut Valley Festival, its official name).