Egelston Township Fire Department Deputy Chief Dan Willea said the Muskegon man brought the grenade, which was live but still had its pin intact, to the station at about 3 p.m. Wednesday, The Muskegon Chronicle reported Thursday.
"He walked up to the desk and said 'I have something I think you're going to want to see,'" Willea said.
Willea said the Michigan State Police bomb squad was called in from Grand Rapids to transport the grenade back to their headquarters, where the device is likely to be subjected to an X-ray and destroyed.
The man said he found the grenade in a storage unit he purchased in an auction.
"He absolutely did the right thing by bringing it in," Willea said.