The Oneota Complex in Wisconsin during the late Woodland / Mississippian period used salt to temper their pottery (Boszhardt 2008). Probably for other uses too, but it's in pottery where we see it salt usage most clearly. There aren't any readily available sources of salt in the Wisconsin though, so the Oneota peoples probably got it through trade from places further south.

In this post, I discuss the salt trade in the Eastern Woodlands and how salt was produced in different areas historically. There's also the coincidentally well-timed Certain Trends in Eastern Woodlands Salt Production Technology, which was published in the September issue of Midcontinental Journal of Archaeology, which I happened to read just after writing the salt trade post. It's mainly about the development of salt pans and related artifacts, but it does have some additional information on some of the sites I mentioned in the linked post, such as the Great Salt Spring.