Hi Susan,
If you go ahead and put [[Category:Johnson Township, Clark County, Illinois]] on the profile of whomever you're working on, then click on the red link that will create on the profile, you'll be taken to an edit page for the category. Once there, you need to put in [[Category:Clark County, Illinois]], and doing that will create the category, as I think we have all US counties set up. Let me know if you need a hand!
