Catholic institutions themselves employ over 1 million people in the United States. That would make the church one of the nation's largest employers, behind only Walmart. It employs far more people than General Electric or McDonald's or GM or the U.S. Postal Service.
A large portion of the church's revenue comes from donations, though it's hard to say how much, exactly: "Anecdotal evidence suggests that America’s Catholics give about $10 per week on average. Assuming that one-third attend church regularly, that would put the annual offertory income at around $13 billion." There's also income from investments and landholding.
There's a much, much longer breakdown of the economics of the U.S. Catholic church from the Economist here. One key detail: "The American church may account for as much as 60% of the global institution’s wealth."