If you've never visited a Wisconsin salt mine that's because all the salt applied to our roads (along with the salt in your shaker) is mined elsewhere: Michigan, Louisiana, Canada, Chile, etc. The exact journey that salt takes can be hard to trace.
As far as road salt goes, each year the Wisconsin Department of Transportation projects how much salt each county will use and signs contracts to supply those needs throughout the winter season. The map on the right shows you the companies that supplied Wisconsin road salt in the 2020-21 season. (Map provided courtesy of WisDOT.)
Like most forms of resource extraction, salt mining can be dangerous. The most recent salt mine disaster in Lousiana was on December 14, 2020 on Avery Island. The roof of the mine collapsed and two workers went missing, and were found dead the next day. The mine received more than 50 safety citations that year, but Cargill said there was "no indication" the safety violations were related to the collapse (source). As more salt mines in the United States shut down, our salt must be imported from other countries. This drives up the cost of salt and the overall carbon footprint associated with it's use.