Cooper & Hewitt partners were iron businessmen who purchased ironworks, property, and iron mines. In 1845, a rolling mill complex was incorporated as the Trenton Iron Company, and in 1847 iron mines at Andover, New Jersey, were purchased. The records consist of two payroll sheets from 1848, as well as eighty-two inbound letters, mostly from 1849 to 1850. The letters are primarily operating reports from the superintendent of the Andover mine.

The Phoenix Steel Company began in the late eighteenth century as a manufacturer of cut nails. It later became a major producer of railroad rails and iron and steel structural members. Their records include minutes (1856-1929); stock ledgers; brief of title papers and property maps; legal and financial correspondence and tax papers; account books; and a works diary.