Mo. Rev. Stat. § 407.070: Petition to extend return date, when and where filed.

At any time before the return date specified in a civil investigative demand issued under section 407.040, or within twenty days after the civil investigative demand has been served, whichever period is shorter, a petition to extend the return date for, or to modify or set aside the civil investigative demand, stating good cause, may be filed in the circuit court of the county where the parties reside or in the circuit court of Cole County.