Whether the noncompete clause is enforceable under Kansas law would depend upon an analysis of its terms, and whether it is reasonable as to geographic area and time, part of an otherwise valid and enforceable contract, and related to a protectable interest of the employer. If you want to know if the clause at issue would likely be enforced by a court, you would have to have the language reviewed by a Kansas employment lawyer.
It sounds like the concern is that you not perform work in the four counties, regardless of where your employer is situated. (That is, you could likely work for an employer which has offices in one of the four counties, provided you did not work on any jobs which were located in those counties.) But that's speculative, as I haven't read the contract language - if you want a definitive answer, you need to have the actual language of the noncompete agreement reviewed by a Kansas lawyer.

