A detection system (10) includes a ranging-sensor (20) and a controller-circuit (32). The ranging-sensor (20) is configured to detect objects (26) proximate to a host-vehicle (12). The controller-circuit (32) is in communication with the ranging-sensor (20). The controller-circuit (32) is configured to determine that a trailer (14) is being towed by the host-vehicle (12) and determine a trailer-distance (42) between the host-vehicle (12) and a front of the trailer (14) based on a distance (28) to a first-group (46) of objects (26) detected by the ranging-sensor (20). The first-group (46) is characterized by a first-distance (48) indicated by the ranging-sensor (20). The controller-circuit (32) determines an axle-distance (56) between the front of the trailer (14) and a trailer-axle (58) based on a second-group (60) of objects (26). The second-group (60) is characterized by a second-distance (62) indicated by the ranging-sensor (20). The controller-circuit (32) determines a trailer-length (16) based on the trailer-distance (42) and the axle-distance (56).