Great Lakes region is the industrial base for the U.S.. Mining, steel mills, machinery manufacturing, automotive manufacturing, tool making all take place here. Minnesota, Wisconsin, Northern Illinois, Michigan, Ohio, Indiana; very large population of machinist in this region. Close to all resources needed for heavy industry from raw suppliers all the way to companies that can build or rebuild machinery for specialized machining operations. Also makes a convenient distribution point for the entire U.S. Logistics and maybe there is a history to barrel making in that state as well.
@Frank Green may be able to shed more light on this topic.