Basic rules of thumb for Wisconsin--
No concealed carry.
No handguns (only) in places that serve alcohol for consumption on the premises, without permission of the owner/manager.
No firearms in state parks unless unloaded and encased.
No firearms in government buildings -- i.e., owned or leased by the state or a municipal government. (Without permission.)
No firearms within 1000 feet of school grounds (grades 1-12) unless unloaded and encased OR unless on private property.
Transport in a vehicle requires the firearm to be unloaded and in a gun case.
Municipalities can regulate the discharge of a firearm, so if you're planning target shooting make sure you know the local law.
There is nothing prohibiting firearms in banks or churches or anywhere else not listed above. Although some municipalities seem to believe they can regulate possession of firearms in their local parks.
Most private businesses don't seem to have a policy prohibiting guns, but if you're told to leave or to remove the gun from the premises, best thing to do is to comply or face a possible trespassing citation.
Keep in mind most Wisconsinites probably haven't seen fellow citizens open carrying, so there's always a chance somebody will not like it. The vast majority of OC experiences in WI are without anything noteworthy happening. Most people either don't notice the gun or give no outward sign of recognition or concern. They just go on doing what they had been doing. Also keep in mind that large areas of Wisconsin during the summer are populated by tourists from Illinois, so draw your own conclusions about that.