By the time of Appo's first incarceration in 1874, Sing Sing was a sprawling, seventy-seven-acre industrial complex, simultaneously a "great human cage" and "a leviathan" factory complex…Inside, horses and wagons moved higher and thither, ship masts towered above the quay walls, and freight trains thundered through the prison grounds. In the age of industry, wrote another observer, Sing Sing was a "vast creative emporium." It was arguably the largest manufacturing complex in the country, if not the world.
The size of Sing Sing's labor force dwarfed those of most American factories.
That's from Timothy Gilfoyle's excellent A Pickpocket's Tale: The Underworld of Nineteenth Century New York.