The Chicago Business Barometer Index declined in June to 66.1 from 75.2 in May, hitting a four-month low, data showed on Friday.
During the second quarter (Q2) of the year, the Purchasing Manager Index (PMI) rose by 7.9 points to 71.1, according to ISM-Chicago.
This marked the highest quarterly reading for the index since Q4 of 1973.
New Orders also fell to a three-month low in June, but surged in Q2 to 73.0, its highest reading since Q3 of 1983.
Meanwhile, the production index fell by 10.6 points this month but rose slightly in Q2 to 67.9.