The Chicago Business Barometer, also known as the Chicago PMI, fell 0.8 index points to 44.3 in January.
Economists polled by the Wall Street Journal forecast a 45.3 reading.
This is the fifth straight reading below the 50 threshold that indicates contraction territory.
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 January is released on Wednesday.
Economists expect the IMF factory index to weaken to 48.0 in January from 48.4% in the prior month.