The Grant County sheriff's office says crews were sent to the farm outside of Lancaster just after 11 a.m. Thursday.
WKOW-TV reports the family was trying to fix an auger in the grain bin that had become stuck. The boy was helping other family members when he became trapped in the half-full bin.
Chief Sheriff's Deputy Jack Johnson says rescuers found the boy around 12:30 p.m. He was pronounced dead at the scene.
The boy's name was not immediately released. Lancaster is about 68 miles southwest of Madison.