With numbers above 50 indicating expansion, the Chicago association's headline business barometer remained positive at 53, but expansion was at a slower pace than July when the headline index registered 53.7.
Among composite indexes, the production index rose from 54.5 to 57.4, while the new orders index rose from 52.9 to 54.8.
The employment index, which dropped in July, rose from 53.3 to 57.1 in August. The inventories index, however, dropped from 52.6 to 51.2.
The Chicago report covers businesses in Illinois, Indiana and Michigan.