I believe you are incorrect. The largest is great barrier in australia, the second largest (which happens to be in North America), is closer to cozumel.
The Belize Barrier Reef - second largest in the world, stretching from southern Quintana Roo, Mexico along the coast of Belize to the Bay Islands of Honduras.
Also, the Florida Keys Reef Tract is the only LIVING coral barrier reef in North America, this is also the third largest barrier reef in the world.
"The reef runs roughly 221 miles down the south-eastern coast of Florida, paralleling the Florida Keys from Key Biscayne off Miami down to the Dry Tortugas, 70 miles west of Key West, from 1 mile to 8 miles offshore."
Please correct me if I am mistaken, thank you.