The train hit two people -- two teens -- who were either on the tracks or too close to them around 5:45 p.m. as Hiawatha train 339 was passing by Conway Road, just north of the Lake Forest Metra station.
Amtrak spokesman Cliff Cole said the accident didn't happen at a crossing, but rather that those hit were trespassing.
The Lake County Coroner said one person died at the scene. Another person was taken to Advocate Condell Medical Center in Libertyville. Their identities have not yet been released.
There were no injuries among the 138 passengers about the northbound train, which had just left Chicago and was scheduled to arrive in Milwaukee about 6:45 p.m., Cole said.
Metra spokeswoman Meg Reile said one Metra train was able to make its way to the Lake Forest station to let out passengers, but all other trains were initially stopped.
Reile said northbound trains were moving at "walking speed," although all southbound trains remained stopped at 7 p.m. Lake Forest police were not immediately available for comment.