The county of Buffalo is bounded as follows: Commencing at a point where the dividing line between ranges twelve and thirteen crosses the southern channel of the Platte River; thence up said channel to a point where the dividing line between ranges eighteen and nineteen intersects the same; thence north along said line to the third standard parallel; thence east along said parallel to the northeast corner of township twelve, north, of range thirteen, west; thence south to the place of beginning.