Many states including WI have what are called "stop and ID laws" which don't require you to carry ID per se, but do require you to identify yourself to a police officer who has reasonable suspicion to believe a crime has or may be taking place.

Here's the WI statute:

Of course, you aren't legally required to tell them anything, however not cooperating will almost certainly prolong your encounter.

Personally, I appreciate knowing I have the right to remain silent and not cooperate, but in practice I don't really mind indulging an officer's curiosity when it's something mundane, particularly if it spares me a more formal interrogation at the police station.

Just remember, it's your choice.