We implanted 2212 juvenile coho salmon (Oncorhynchus kisutch) 55 to 111 mm with Passive Integrated Transponder (PIT) tags to determine their growth, overwinter survival, and emigration timing from the East Twin River and its tributary, Sadie Creek, on Washington's Olympic Peninsula. Detections of tagged fish by instream antennas revealed that a much higher proportion of juvenile coho salmon emigrated to the sea in the fall than during the spring. Fall emigrants predominantly originated from East Twin River (96.6%) whereas Sadie Creek coho salmon remained in-stream to overwinter where they grew faster and became larger when compared to smolts from East Twin River. Results suggest that fish size in the fall and location in the watershed may influence emigration timing.