From the first (1857) through the fifth (1876) editions of his Chronology of Paper and Paper-Making
Joel Munsell stated:
"A paper mill went into operation at Pittsburgh, Pa., with a steam engine of sixteen-horse power, on the principle of Oliver Evans, which employed forty persons, consuming 10,000 bushels of coal and 230,000 pounds of rags per annum; and manufactured $20,000 worth of paper annually." That Munsell repeated this in all five editions would suggest that he felt his information was reliable; however, I have not been able to learn more details about the particular paper mill. The unidentified steam-powered paper mill would have necessarily been mechanized, and would therefore have predated Thomas Gilipin's mill that began operation in 1817
which is authoritatively considered the first mechanized paper mill in the U.S. Therefore it is possible that Munsell was simply wrong.
Or was he?