Ambulance staff informed police of the death of the boy, who was eight months old, at around 10:30 BST on Wednesday.
Officers were called to Brownhills Road in Newton Abbot, and subsequently closed off the road.
A spokesman for Devon and Cornwall Police said a 27-year-old man had been taken into custody in relation to the death.
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Scenes of crime officers and police attended the house to undertake initial investigations, where they found a sibling of the child along with two adults.
Devon and Cornwall Police said they were not looking for anyone else in relation to the case.
Police are investigating the "suspicious" death of a baby boy in Devon.