The Chicago Business Barometer, also known as the Chicago PMI, rose to 60.3 in May from 56.4 in the prior month.
Economists polled by the Wall Street Journal forecast a 55.9 reading.
The index is produced by the ISM-Chicago with MNI. It is released to subscribers three minutes before its release to the public at 9:45 am Eastern.
The Chicago PMI is the last of the regional manufacturing indices before the national ISM data for May is released on Wednesday.
The prior business surveys showed a sharp slowdown in business activity.
Economists surveyed by The Wall Street Journal have forecast a 54.5% reading for the closely-watched ISM manufacturing index in May after a 55.4% reading in the prior month. That was the lowest reading since July 2020.