There are two types of alligators: the American alligator and Chinese alligator. The critically endangered Chinese alligator lives in a more extreme climate, while the American alligator prefers the milder climate of the southeastern United States. Alligators are ectotherms -- they regulate their body temperature externally -- so climate is important to them.
Alligators are descended from dinosaurs and have been around for millions of years. Since they're cold-blooded animals, they don't care for cold climates. In the U.S., the southeastern part of the country provides the ideal habitat. The Atlantic states -- specifically the Carolinas through Florida -- as well as the Gulf Coast and Texas all provide the ideal environment for the American alligator.
Cold Blood, Warm Sunshine
The alligator's surroundings help him regulate his body temperature. He'll warm up by basking in the warm sun, and if he gets a bit too warm, he'll open his mouth while he soaks up the rays. He's not looking for dinner to crawl in, but instead, is cooling himself, much as your dog regulates his temperature by panting. The gator may appear to be a lazy beast, but his cold-blooded ways mean he doesn't have a lot of energy to spare.
Swimming and Burrowing
The American alligator lives in wetlands, rivers, swamps and other freshwater sources, as well as brackish waters. The water helps him cool off when it becomes especially hot, or he'll withdraw to whatever shade is available to become more comfortable. He'll likely dig a burrow for himself, using his feet and mouth to tunnel through a mud bank. The burrow serves double duty: it offers warmth during cooler times and helps the local wildlife by holding water during droughts. Not only is the hole home for the gator and its offspring, other local wildlife lives in or near the hole until rain returns to the area.
The Chinese alligator is smaller than his American cousin and has a much more limited range. He passes his days in eastern China, around the Pacific coast of the Yangtze River. The river, swamps, marshes and lakes of the area provide him the water he needs, however, because of the cold temperatures, this guy hibernates in underground tunnel systems. He emerges in May and passes the summer sunbathing to warm himself. There are about 200 of these guys left in the wild.