Mo. Rev. Stat. § 140.195: Entry on property not trespass, when.

Any collector, agent of any collector, tax sale purchaser, or agent of any tax sale purchaser performing duties under this chapter shall have the lawful right to enter upon the land of another without being guilty of trespass, if he or she is in the course of providing or attempting to provide notice of a tax sale or tax sale redemption rights and it is necessary to enter upon such land to provide, serve, or post such notice.