In a Facebook post, Ald. John Arena (45th) announced that the City Council passed the landmark designation.
"Thank you to everyone who supported this action to preserve a historic building that is a cornerstone of our community," Arena wrote. "May the light from the projection booth shine long and bright for generations to come."
The Chicago Commission on Landmarks voted unanimously in March to recommend the city's zoning committee and the City Council make it more difficult to alter both the inside and the outside of the theater, which was built in 1919 and 1920.
The theater has served as a centerpoint of the Chicago independent film community and a key venue for up-and-coming indie musicians, according to its website.
"In the eyes of the community it has been a landmark for years and this just formalizes that," Arena said at the time.
Efforts to landmark the Portage Theater began more than a year ago when the Chicago Tabernacle Church planned to purchase the theater in the heart of the Six Corners Shopping District over the objections of Arena, the business community and several neighborhood groups.
Instead, the church found another home, and Eddie Carranza, the owner of the Congress Theater in Logan Square, bought the theater.
In addition to the facade, the landmark designation requires the building to have a marquee. Because the current marquee isn't original, it could be replaced, Arena said.
The designation will also protect both the inner and outer lobby of the theater, as well as the interior of the theater, with its intricate scrolls and designs.
The theater's owner would be allowed to remove the 1,300 seats in the theater because they aren't original, Arena said. However, the designation requires that it continue to be used as a cinema.