The Chicago Business Barometer Index surged in May to reach a reading of 75.2 from a level of 72.1 in April, data showed on Friday.
The Purchasing Manager Index (PMI) reached its highest level since 1973, according to ISM-Chicago.
Robust demand helped boost the business activity, with the new orders index rising by 7.7 points in May to its highest level since December 1983.
Meanwhile, the production index declined by 2.3 points.