Mo. Rev. Stat. § 50.750

Every county officer, agent or any governing body of any county in this state authorized to make purchases for use of their county shall purchase and use only those materials, products, supplies, provisions and other needed articles produced, manufactured, compounded, made or grown within the state of Missouri, when they are found in marketable quantities in the state and are of a quality suited to the purpose intended, and can be secured without additional cost over foreign products or products of other states; provided, however, that quality and fitness of articles shall be considered in purchasing or letting contracts for articles herein mentioned.