This is the 1307th most frequent Polish word.
mieszkańcami
"Residents" or "inhabitants."
In this sentence, "mieszkańcami" is used in the instrumental case to indicate the group of people ('residents') with whom an action ('talking') was performed.
Rozmawialiśmy z mieszkańcami miasta o ich problemach.
We talked with the residents of the city about their problems.
Here, "mieszkańcami" is also in the instrumental case, showing the association between the entity ('villagers') and the event ('meeting').
Spotkanie z mieszkańcami wsi odbędzie się w sobotę.
The meeting with the villagers will take place on Saturday.
In this case, "mieszkańcami" is again in the instrumental case, used to represent the parties involved in a relationship ('residents of different districts').