The Annual Knox County Chamber of Commerce Watermelon Festival and Great American Grill-Off get underway today. (Saturday) The Watermelon festival runs from 8:00 AM until 8:00 PM on Patrick Henry Square in downtown Vincennes. Among the activities is a free concert from 1:00 until 3:00 PM. The Great American Grill-Off competition kicks-off at 7:00 AM. There will be kids' games, crafts & flea market, food booths and free watermelon provided by Nowaskie Melons.