Mo. Rev. Stat. § 416.545: Venue of actions.

Except as otherwise provided under sections 416.450 and 416.455, any suit brought under the provisions of sections 416.410 to 416.560 shall be filed in the county in which the cause of action accrues or in the county where the plaintiff resides, and if there be other defendants in the action who are residents of the state of Missouri, then the action shall be brought in any county in which any one of said defendants resides, or in the county within which the plaintiff resides and the defendant may be found.