Missouri does not yet have a preemption for open carry.
This means county and cities can ban it at their own choice.
There are four basic types of restriction.
1 None allowed at all
2 allowed with owners written permission
3 allowed with a ccw (Missouri accepts all states so indy is all good)
4 allowed, no conditions.
The problem is, you don't know where and what is legal on one side of the street is not legal on the other side of the street, LITERALLY.
I would highly recommend you consider CCW unless you want to pan out your entire trip and not deviate as you will have to check all the codes for the cities you will visit.
It is not common at all in the urban areas and the odds of you being approached by an officer who is not up to speed with it being legal are very high. in the more rural parts of the state, most folks are not going to take much notice.