Officials say the Manhattan-bound train hit the person Monday morning. The investigation is causing delays of up to 10 minutes on westbound and eastbound trains.
Metro-North police are trying to determine the person's identity and why the person was on the tracks.
Officials say eastbound trains won't be stopping at the Noroton Heights, Darien or Rowayton stops. Riders can take an eastbound train to South Norwalk and transfer to a westbound train to get to those three stations.
Commuters at the three affected stations can take a westbound train to Stamford and transfer to an eastbound train for locations east of Darien.