The Michigan DNR’s page on the Eastern Garter Snake (Thamnophis sirtalis) says that the Eastern Garter is Michigan’s most common snake, inhabiting both peninsulas and even urban areas. Wikipedia notes that they are often mistakenly called garden snakes or gardener snakes and the UM Animal Diversity Web entry for garter snakes adds more info and lots of photos and says that although there are very rare cases of allergic reaction from bites from people handling garter snakes, these reptiles deserve their reputation as a harmless and beneficial low-level predator. Be warned if you handle them that their main defense is a stinky secretion!
This picture is part of a cool set of photos from the Bald Mountain Recreation Area (slideshow). Alanna also commented that she thinks snakes are cool. If you do too, you’ll probably enjoy the Snakes of Michigan page from Snaketamers. It lists Michigan’s 18 species of native snakes (with photos). You can also check out the listing of Michigan’s Snakes from the DNR.