Forming a Posse in Red Dead Redemption (Xbox 360): Not Possible

You cannot form a posse in the original Red Dead Redemption (Xbox 360/PS3).

• The Posse system was introduced in Red Dead Redemption 2 (2018) — Online mode only.
• RDR1 multiplayer (Free Roam) had no persistent group system — just a 16-player session with friendly fire toggle and basic matchmaking for modes (Gun Rush, Capture the Bag, etc.).
• No posse camps, shared XP, or posse missions.

What You Can Do in RDR1 Multiplayer

• Free Roam: Ride together, hunt, clear gang hideouts, grief/cooperate.
• Competitive Modes: 8v8 team matches.
• Co-op Missions: "Outlaws to the End" DLC (6 missions, 2–4 players) — closest to posse play.

RDR2 Online (Current)

• Form a Permanent Posse ($200 in-game) or Temporary Posse (free, session-based).
• Posse Leader manages ranks, camp, supplies, roles (Trader, Collector, Bounty Hunter, Moonshiner).
• Cross-play: PS4/5, Xbox One/Series, PC, Stadia.

If you want posse gameplay, play Red Dead Online (RDR2). RDR1 multiplayer is a ghost town (servers up but empty).