But you didn't request the wording for a species native to Chicago and X, just one native to Chicago. And there is a word for that. IF you have two small endemic populations, there is generally a reason for that, namely the species was once more widespread and has been extirpated from elsewhere in between, in which case its distribution is relictual and it IS properly called an endemic, just not of Chicago alone, but of the larger area, or it has been introduced in the second place, in which case it can still be endemic to the first, or it is actively speciating due to a founder floundering there, or its endemism is edaphic, or otherwise than geographically defined.
Endemism is the word.
"Endemic to X" means "native to only X", which is not what I was looking for. I was looking for a way to say "Native to X but not all of Y" where X is a subregion of Y. The region an animal is endemic to is not usually a region that would get a list in the "Animals native to X" collection, so it would have to appear on multiple lists, or on one more general list (which loses precision).