Mo. Rev. Stat. § 221.044: Persons under eighteen may not be confined in adult jails, exceptions .

No person under the age of eighteen years, except those transferred to the court of general jurisdiction under the provisions of section 211.071, shall be detained in a jail or other adult detention facility as that term is defined in section 211.151. If a person is eighteen years of age or older or attains the age of eighteen while in detention, upon a motion filed by the juvenile officer, the court may order that the person be detained in a jail or other adult detention facility as that term is defined in section 211.151 until the disposition of that person's juvenile court case.