The Chicago purchasing managers' index (PMI) has dropped from 58.7 to 51.6 in June. The index attempts to capture business conditions across Illinois, Indiana and Michigan.
As the number is still higher than 50, that still implies an expansion, but the rate of expansion is much slower than before. Economists had anticipated some slowdown, predicting a drop to 56.0.
Last month saw the biggest rise in Chicago PMI in 30 years.