Allen County sheriff's deputies responded to a report of a house fire at 11:18 p.m. Thursday in the northern part of the county and found a mobile home engulfed in flames, said Victor Hopkins, spokesman for the sheriff's department.
The names of the victims were not immediately released.
Sheriff's deputies tried to enter the trailer but were driven back by flames, Hopkins said.
One man escaped the fire and was taken to a hospital in serious condition with deep cuts to his arms.
Firefighters found the bodies of a woman, a 10-month-old girl and a 3-year-old boy. A family dog also died.
The fire left the pink and blue trailer in a pile of ruins. Smoke and flames were still billowing from the home early Friday.
The Allen County arson team, the Allen County Sheriff's Department, the St. Joseph Township Fire Department and the Allen County coroner's office were investigating.
Fire investigators have not determined a cause of the fire.
