The county of Rush is bounded as follows: Commencing where the east line of range sixteen west intersects the third standard parallel; thence south with said range line, to the north line of township twenty south, range sixteen west; thence west with said north line of township twenty south, of range sixteen west, to the east line of range twenty-one west; thence north with said range line, to the third standard parallel; thence east with said parallel line, to the place of beginning.