With numbers more than 50 indicating expansion, the Chicago association's headline business barometer remained dropped from 53 in August to 49.7 in September.
Among composite indexes, the production index dropped from a reading of 57.4 to 55.4, while the new orders index fell sharply from 54.8 to 47.4.
The employment index showed growth in September but at a slower pace than the previous month with the index sliding from 57.1 to 52.
The Chicago report covers businesses in Illinois, Indiana and Michigan.
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