The discovery was made around Wednesday afternoon by a maintenance worker in the building, WBBM-TV, Chicago, reported. Police arrived at the building around 3 p.m. and Bomb and Arson Unit technicians removed the grenades from the building and safely disposed of them elsewhere, officials said.
Building owner Ron Kita said he thought the grenades were fake.
"I was surprised. To my knowledge, they weren't real. My brother said he used to play with them as a child," Kita said.
Kita's late father served in the army.
"Who knows what older veterans have in their homes," said resident Tina Delacruz. "It's a little unsettling because I live here and I've lived here for three years."