Kan. Stat. § 18-103
The county of Atchison is bounded as follows: Commencing at the southeast corner of Doniphan county; thence with the south boundary of Doniphan county, to the township line between townships four and five south; thence west with said township line between townships four and five south, to the range line between ranges sixteen and seventeen east; thence south with said range line, to the southwest corner of section nineteen, of township seven south, of range seventeen east; thence east with the section lines, to the intersection with the western boundary line of the state of Missouri; thence north with said western boundary line of the state of Missouri, to the place of beginning: Provided, That such boundaries shall include land adjacent to such county and ceded to the state of Kansas by the state of Missouri but shall not include land ceded by this state to the state of Missouri: Provided further, That the north line of Atchison county in the northeast corner of the county shall be the south line of Doniphan county as provided by the law setting the boundaries of Doniphan, as amended, so as to include land ceded to this state by the state of Missouri.
K.S.A. 18-103