Not sure whether I missed this or it hasn't been shared yet, but there is a map of free wi-fi hotspot locations in Michigan being populated here:

http://cngis.maps.arcgis.com/apps/webappviewer/index.html?id=0d69accbb5ff422a82eccc2c9101b69d

To add your library or branch, click the i in the upper right corner and link for a form to be added.