If it did play on "Disneyland," call it what you will, as it was one of the longest running programs on TV, playing on all 3 networks, under several different titles, then there are two possibilities for the time period mentioned. One is "Elfego Baca" with Robert Loggia in the title role, and the other is "Texas John Slaughter" with Tom Tryon in the title role. Good luck and happy hunting!
It could be either of these, but neither of them seems to have a young boy as a major character. I remember that the villain was always a menace to the kid, but the Marshal would always show up to help. I think there was some reason that the Marshal couldn't arrest the villain. I think all he could do was show up and tell the bad guy to leave the kid alone.