Any county may place money of the county which it has determined is not needed for current operations in obligations described in Section 15, Article IV, Constitution of Missouri, outright or by repurchase agreement. Such obligations and agreements shall be purchased through institutions in the county whose deposits may be insured by an agency of the United States government, hereafter referred to as federally insured institutions, provided the county determines such purchases to be in the best interest of the county as determined by the county treasurer. When such federally insured institutions are unwilling or unable to provide such obligations and agreements, the county may purchase them from federally insured institutions in any adjacent county in Missouri. The investment authority granted by this section shall be in addition to the investment authority otherwise granted a county by law.