adding interactive graphic to custom map

I want to add information to a map I upload.
Specifically, I want the reader to be able either to click on or hover over a town on the map and see information I provide.
The maps I upload are of Counties in the US so are not available from Google Maps or the like.
The information I want to add is not a location but something like a tax rate which needs to be entered manually.
I have searched and searched for days but not found a way to do this.
Any help would be most gratefully received!!!