Mo. Rev. Stat. § 534.250: Persons having settlement on public lands may maintain action, when.

Every person who shall have a settlement or field on public land, who shall reside on or be in possession of the same at the time of the forcible entry and detainer, or unlawful detainer, shall have the same remedy as is herein provided in such cases, against any person who shall make such unlawful entry upon him; provided, that any person having authority from the United States, or lawfully claiming under them, shall have power to enter into such land.