Rev. George W. Daniels, senior pastor of First Baptist Congregational Church, 1613 W. Washington Blvd., said damage appeared extensive.
No one was hurt.
Daniels informed about 1,000 congregation members after discovering the damage on Thursday.
"They're saddened by it," he said. "It's just like your home. If something happens to your home, naturally you're concerned about how bad the damage is and how much it's going to cost."
Daniels said he was both happy and sad when he discovered what happened: sad because of the damage caused but happy that no one was killed or injured.
"You can replace things but you cannot replace life," he said.
A structural engineer today will determine the extent of the damage and if services can continue to be conducted in the main sanctuary, Daniels said. If they cannot, they will be transferred to a fellowship hall on the premesis, he said.
Construction on the church began in 1869 and was completed in 1871, he said. It was named a state landmark in 2006 and a National Historic Landmark the following year, he added.
The building survived the Great Chicago Fire of 1871 and is said to have temporarily housed government workers during the reconstruction of their offices. It originally was built as the Union Park Congregational Church, according to the AIA Guide to Chicago and designed by Gurdon P. Randall, who designed Northwestern University's University Hall in Evanston.
Daniels' congregation has been in the church building since 1970.