One Iowa city is now officially home to the largest cereal plant not just in the United States, but the entire world!. The Quaker Oats Plant in Cedar Rapids, IA is officially the largest cereal plant in the world, per the World Record Academy. The towering structure is the 4th-tallest building in Cedar Rapids, and is located on the north end of town, separated from the downtown area by I-380 with the building's west side sitting along the gorgeous Cedar River.