Kate Fratt Memorial Parochial School was a school for 99 years, from 1918 to 2017.
It's now the Fratt Condominiums and an open house on Saturday gave the public one last chance to see the building before the classrooms become homes.
The school also had the name St. Francis and was part of the Billings Catholic Schools.
"Our kids went to the school and I've watched this building since I was a kid," said Russ Fagg of Fagg Family Properties. "I've always liked this building and I thought that building needs to be saved."
Fagg Family Properties remodeled the building and all 13 units have been sold.
"We're biased but we just think they turned out awesome," Fagg said. "So there's hardwood floors on floors two and three, 11 to 13-foot ceilings, open floor plans."
"It's so fun to see how sturdy this building is and just the architecture of it," said Shelby Williams, Century 21 Realtor, who worked with the Faggs on the project. "And that hand-made product that went into this in 1918. Like it's amazing to see it now and still standing and going to good use"
Williams says there are good reasons why the condominiums sold.
"Its proximity to downtown," Williams said. "It's location. The space around it. The beauty of the building. The historic site. Parking and the patio area. And just has all the amenities to easily live, work, and play downtown."
Many of those at the open house are former students.
"We're at our 60th class reunion," said Lynnette Shaurette, who visited her old school with some of her high school classmates and was a Fratt student in the 1950s. "I am thrilled that something has been done."
"It seems like they left a lot of pretty original," said Joe Stribley, a Fratt student in the 1960s. "Pretty cool."
Stribley's late father started at Fratt in 1918.
He also has three sisters who went to the school.
Hollywood screenwriter T.J. Lynch and his wife Maggie purchased what he remembers as the 4th-grade room on the second floor.
"In some ways, it makes me feel old," Lynch said. "And in some other ways, it makes me feel immortal."
"I think this project will spark some more condos and downtown living," Williams said.
"God willing, it'll be here 100 years from now, people will be enjoying it," Fagg said.
Williams said some will start moving in this week.
The building at 235 North 32nd Street is on the National Register of Historic Places.