I checked the city ordinances and see nothing concerning OC, so you should be good to go.
WARNING: I am not a lawyer, please check municipal codes for yourself to be sure.
Here is Joplin's posted city code concerning weapons:
Sec. 82-191. Unlawful use of weapons; exceptions.
(a)For the purposes of this section, terms and phrases used herein shall have the definitions given them under RSMo 571.010.
(b)A person commits the crime of unlawful use of weapons if he knowingly:
(1)Carries concealed upon or about his person a knife, a firearm, a blackjack or any other weapon readily capable of lethal use.
(2)Sets a spring gun;
(3)Discharges or shoots a firearm into a dwelling house, a railroad train, boat, aircraft or motor vehicle as defined in RSMo 302.010, or any building or structure used for the assembling of people;
(4)Exhibits, in the presence of one or more persons, any weapon readily capable of lethal use in an angry or threatening manner;
(5)Possesses or discharges a firearm or projectile weapon while intoxicated;
(6)Discharges a firearm within 100 yards of any occupied schoolhouse, courthouse, or church building;
(7)Discharges or shoots a firearm at a mark, at any object, or at random, on, along or across a public highway or discharges or shoots a firearm into any outbuilding;
(8)Carries a firearm or any other weapon readily capable of lethal use into any church or place where people have assembled for worship, or into any school, or into any election precinct on any election day, or into any building owned or occupied by any agency of the federal government, state government or political subdivision thereof;
(9)Discharges or shoots a firearm at or from a motor vehicle, as defined in RSMo 301.010, while within any city, town or village, and discharges or shoots a firearm at any person, or at any other motor vehicle, or at any building or habitable structure, unless the person was lawfully acting in self-defense;
(10)Carries a firearm, whether loaded or unloaded, or any other weapon readily capable of lethal use, into any school bus, or onto the premises of any function or activity sponsored or sanctioned by school officials or the district school board.
(c)Subsections (b)(1), (3), (4), (6), (7), (8), (9), and (10) of this section shall not apply to or affect any of the following:
(1)All state, county, and municipal peace officers possessing the duty and power of arrest for violation of the general criminal laws of the state or for violation of ordinances of counties or municipalities of the state, whether such officers are within or outside their jurisdictions, or on-duty or off-duty, or any person summoned by such officers to assist in making arrests or preserving the peace while actually engaged in assisting such officer;
(2)Wardens, superintendents, and keepers of prisons, penitentiaries, jails and other institutions for the detention of persons accused or convicted of crime;
(3)Members of the armed forces or national guard while performing their official duty;
(4)Those persons vested by article V, section 1 of the state Constitution with the judicial power of the state and those persons vested by article III of the Constitution of the United States with the judicial power of the United States, the members of the federal judiciary;
(5)Any person whose bona fide duty is to execute process, civil or criminal;
(6)Any federal probation officer;
(7)Any corporate security advisor meeting the definition and fulfilling the requirements of the regulations established by the board of police commissioners under RSMo 84.340; and
(8)Any state probation and parole officer, including supervisors and members of the board of probation and parole, authorized to carry a firearm pursuant to RSMo 217.710.
(9)Any coroner, deputy coroner, medical examiner, or assistant medical examiner.
(d)Subsections (b)(1), (5), (8), and (10) of this section do not apply when the actor is transporting such weapons in a nonfunctioning state or in an unloaded state when ammunition is not readily accessible or when such weapons are not readily accessible. Subsection (b)(1) of this section does not apply to any person 21 years of age or older transporting a concealable firearm in the passenger compartment of a motor vehicle, so long as such concealable firearm is otherwise lawfully possessed, or when the actor is also in possession of an exposed firearm or projectile weapons for the lawful pursuit of game, or is in his or her dwelling unit or upon business premises over which the actor has possession, authority or control, or is traveling in a continuous journey peaceably through this state. Subsection (b)(10) shall not apply if the firearm is otherwise lawfully possessed by a person while traversing school premises for the purposes of transporting a student to or from school, or possessed by an adult for the purposes of facilitation of a school sanctioned firearm-related event.
(e)Subsections (b)(1), (8), and (10) of this section shall not apply to any person who has a valid concealed carry endorsement issued pursuant to RSMo 571.094, or a valid permit or endorsement to carry concealed firearms issued by another state or political subdivision of a state.
(f)Any person violating this section shall be punished upon conviction thereof as provided by section 1-5.
(Ord. No. 97-128, § 1, 8-4-97; Ord. No. 2003-174, § 2, 10-6-03)
Subsection (e) (in green) exempts CCW holders from the above (which is already preempted by state law so you'd be good to go regardless of what the city code says), but I see nothing concerning OPEN CARRY in the entire thing. Therefore, OC should be good regardless of your residency of any state.
I would reccommend going to municode.com and printing out the ordinance for yourself and carrying it with you just in case you are hassled. This way, if you encounter an uninformed officer, you can ask what part of the law you are breaking, and he should be unable to point it out. Therefore, if he can't show you what law you are breaking, there is no grounds for detention, much less arrest.
Good luck, and enjoy your visit!