The Michigan Herps page on Michigan’s Frogs & Toads says that misidentification is common – the trick is the fold of skin running from their eardrum to their back. The UM Animal Diversity Web entry for Lithobates clamitans (green frog) says you can find them all over the eastern US and that:
Green frogs are found in a wide variety of habitats that surround most inland waters, such as: swamps, wooded swamps, ponds, lakes, marshes, bogs, banks of slow moving rivers and streams, oxbow lakes, sloughs, and impoundments. Juveniles may disperse into wooded areas or meadows during times of rain. Green frogs overwinter in the water usually buried in the substrate.
Green frogs produce as many as six different calls. Males attracting a mate give an advertisement call and a high-intensity advertisement call. Their advertisement call has been compared to the pluck of a loose banjo string. Male frogs defending a territory from an intruding male usually give aggressive calls and growls. The release call is given by non-receptive females and by males accidentally grabbed by another male. Finally, the alert call is given by males and females when startled or attacked by a predator.
Green frogs have an excellent sense of vision and use this to detect and capture prey.
More about Michigan’s animals from Michigan in Pictures.