RootsMagic, like many family tree programs, seems to rely on a flawed model of place name structures for the US: municipality, county, state, coutry..
How do RootsMagic "old hands" handle this?
For your specific example, I would enter it as Edgerton, Wisconsin. And often that is the final answer because the nature of place names and their sources is often such that the likelihood of ever determining the county is nil. Edgerton,, Wisconsin with a double comma is awful. Edgerton, Dane or Rock County, Wisconson is accurate from a technical point of view, but adding the county names does not actually add any new information and I think it reads terribly. And I think it's pretty terrible that RM's Gazetteer does not alert you to the possibility of two counties. The unwary RM user might easily use the Gazetteer to convert Edgerton, Wisconsin into Edgerton, Rock County, Wisconsin, and your equally unwary reader might then assume that the event did indeed take place in Rock County even though you have no evidence to support such a conclusion.
I omit "United States" for locations in the United States of America except in the very rare case where there might be some confusion. For example, I don't think that Atlanta, Georgia or Atlanta, Fulton County, Georgia is very likely to be confused with the country of Georgia in the Caucasus region of Eurasia. Except in the rarest of occasions, I think including the United States of America in place names is pedantic, overbearing, dull, nit-picking, boring, fussy, overly punctilious, and basically just awful.
I always include County (or Parish for Louisiana) as a part of the place name when the county is known. The first reason is that that's the way real people speak of county names. I live in Knox County, Tennessee. I would never say that I live in Knox, Tennessee nor would anybody else who lives here. We have Knox County schools, not Knox schools. We have the Knox County Sheriffs Department, not the Knox Sheriffs Department. Etc.The second reason is that without the word County there are numerous cases where the name of a county is also the name of a different political subdivision, and without the inclusion of the word County in the place name it can be totally ambiguous to which political subdivision the place name is referring.
This comes back to your initial comment about family tree programs relying on a flawed model of place name structures for the U.S.A. My personal belief is that the model is even more flawed for place name structures outside of the U.S.A. But to a certain extent, this is not the fault of the family tree programs. Rather, it's the fault of the flawed model. But the problem is that there really isn't an unflawed model. That leaves the family tree programs in the terrible position either of supporting an extremely flawed model or of supporting no model whatsoever.
RM supports an extremely flawed model, but that doesn't mean you have to use the flawed model. You can enter place names any way you wish. Just turn County Check off and use the Gazetteer as an extremely useful but very fallible research tool.
I'm not sure how to rectify the situation. For sure, a new place name model is needed. But whether such a model should ever come into existence or not, the one thing I think that all family tree programs could do that would best address the problem would be to separate the storage of place names from the way place names are displayed. That is, family tree programs could support storing place names in a highly structured way where various political subdivisions (including unknown ones such as your unknown county) are clearly identified. Having stored place names in this highly structured way, family tree programs could then support place name templates that the user could use to specify how various place names should be displayed. Of course, for this to happen the whole genealogy world would have to agree on the standard (including Family Search FamilyTree would have to support and use the standard), GEDCOM or some GEDCOM successor would have to support the standard, and all family tree programs and web sites would have to support the standard. So such a standard is not going to happen.
I can't end without making a final comment about how badly flawed is the model of place name structures. As I said, I don't usually include "United States" in place names. But if I did, I would include "United States of America" which is the correct and official name of my country. Many countries of the world have "United States" as a part of their place name. For example, the official name of our neighbor to the south when translated from Spanish into English is United States of Mexico.