The All About Birds entry for the Great Egret says:
A large white heron, the Great Egret is found across much of the world, from southern Canada southward to Argentina, and in Europe, Africa, Asia, and Australia. It’s the largest egret in the Old World, and thus has garnered the name Great White Egret. In the New World, however, the white form of the Great Blue Heron is larger. In the United States, the Great Egret used to be called the American Egret but that was hardly appropriate, since its range extends beyond the Americas and indeed farther than other herons.
The Great Egret (Ardea alba) entry on the UM Zoology Animal Diversity Web adds that the ideal location for great egrets is near any form of water. Streams, lakes, ponds, marshes and wooded swamps and wetlands are the preferred location for great egrets and other heron species. There is (of course) more on Wikipedia and here’s a sweet video of a great egret nesting site along Lake Huron.
Check out many more Michigan Birds on Michigan in Pictures!