Flight Crew Air Transport Pilot (ATP)
Communication Breakdown; Situational Awareness
Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Weight And Balance
General None Reported / Taken
Company Policy; Procedure
We were preparing to operate [the] flight.  The Ramp Lead came to the flight deck to give us the Load Sheet; and asked if we had brought the aircraft in from ZZZ.  I told him that we had operated that flight.  He then informed us that the ramp personnel in ZZZ had not unloaded the aft cargo compartment when the aircraft arrived in ZZZ; as there were 13 ZZZ tagged checked bags in the aft cargo compartment that he discovered when we arrived in ORD. This caused us to operate ZZZ-ORD; with 390lbs of undocumented bags in the aft cargo compartment.  Not knowing these bags were onboard then caused us to have inaccurate weight and balance information for this flight; including an inaccurate takeoff trim setting.Suggest having the ramp personnel double check the aft cargo compartment when an aircraft arrives at the gate.
EMB-170 Captain reported ramp personnel discovered bags had not been unloaded from the aft cargo pit at the previous airport. This caused the aircraft to operate with 390 lbs of undocumented bags on the flight to ORD.