After looking at Jefferson county city ordinances the only city I found that plainly says no is Pevely. I know others have said no go in Arnold but I can't find where they found it. Instead of posting each link here is the section numbers of each city minus olympian village. Please forgive my spelling and punctuation this is off my cheat sheet I can email you copys of ordinace file if you want off my cheat sheet.
Pevely NO 210.250
Herky ok 210.010
Festus Ok Sec. 18-149.
desoto ok SECTION 215.240
arnold ok Sec. 17-21
crystal city ok Sec. 17-94
Repomaster:
where are you reading where it states open carry is legal in Arnold? Quote: but nothing contained in this section shall apply to legally qualified sheriffs, police officers and other persons whose bona fide duty it is to execute process, civil or criminal, make arrests, or aid in conserving the public peace, nor to persons traveling in a continuous journey peaceably through this state.
Sec. 17-21. Dangerous and concealed weapons; prohibitions concerning.
If any person shall carry concealed upon or about his person a dangerous or deadly weapon of any kind or description, or shall go into any church or place where people have assembled for religious worship, or into any schoolroom or place where people are assembled for educational, political, literary or social purposes, or to any election precinct on any election day, or into any courtroom during the sitting of court, or into any other public assemblage of persons met for any lawful purpose other than for militia drill, or meetings called under militia law of this state, having upon or about his person, concealed or exposed, any kind of firearms, bowie knife, springback knife, razor, metal knucks, billy, sword cane, dirk, dagger, slingshot or other similar deadly weapons or shall, in the presence of one or more persons, exhibit any such weapons in a rude, angry or threatening manner, or shall have any such weapon in his possession when intoxicated, or directly or indirectly, sell or deliver, loan or barter to any minor any such weapon, without the consent of the parent or guardian of such minor, he shall, upon conviction, be deemed guilty of a misdemeanor; but nothing contained in this section shall apply to legally qualified sheriffs, police officers and other persons whose bona fide duty it is to execute process, civil or criminal, make arrests, or aid in conserving the public peace, nor to persons traveling in a continuous journey peaceably through this state.
(Ord. No. 2.8 (Bill No. 29), § 1, 11-16-72)
State law reference--Concealed weapons, RSMo § 564.610