The Militia Act, passed on May 14th begins with a section headed "Military Districts." Section 1 states, "All able-bodied free white males between the ages of eighteen and forty-five years, who shall be enrolled, or liable to military duty, under the provisions of this act, shall constitute, be known and designated as the "Missouri State Guard;" and the State of Missouri is hereby divided into the nine military districts and divisions, as follows, viz:"

Then sections 2 - 10 spell out the counties that are in each of the districts. The ninth district is listed in section 10:
"The counties of St. Louis, Washington, Franklin, Jefferson, and Crawford, shall constitute the ninth military district, and the inhabitants thereof liable to military duty shall compose the ninth military division."

Hope that this helps.