There are fresh and salt water crocodiles, the salt ones tend to be larger and live pretty much where they please. Fresh ones are usually smaller, less dangerous and prefer lakes and rivers.
Crocodiles in general, yes. And you have touched on the distribution pattern for Crocodylus in general*. The other 3 American species of Crocodylus (Orinoco, Cuban, Mexican/Morelet's) do tend to fresh water. But in the Americas, it's C. acutus that's the dominant species and the Florida subspecies of acutus is found pretty exclusively either on Gulf beaches or river estuaries on the West (Gulf) Coast**. It's how acutus got to the Caribbean Islands (before they was exterminated there). Gators (and Caimans), on the other hand, don't like salt water- they lack the salt elimination glands near their eyes that Crocs have.
Also, realize that Southern Florida is the ONLY place in the world where Crocodiles and Alligators can be found in the same general area.
* However, it does sound like you're using the Australian situation as your template, where the difference between the two species (C. porosus & C. johnsoni) is more obvious. Same with South/SouthEast Asia. But Africa is a bit more complicated.
** There's actually a breeding colony of Crocs that hang around the mouth of the discharge stream from a nuclear power plant.