As Maryland Historical Society librarian Francis O'Neill described the winding route to reconstructing the history of Baltimore's homes, a small but eager crowd paid close attention. No one made for the exits, even as he laid new twists on old turns.

"We're not Google," said his colleague, Eben Dennis. "There's not one place you can plug in a keyword and get a photo."

But for those willing to put in some effort, the society has almost a million pictures of buildings from the city and beyond. After an introduction from O'Neill and Dennis, some amateur researchers set straight to work, poring over old insurance maps and digging into census records to work out what stood on the site of their homes and who lived there.

The historical society has pictures and other information on buildings from the grandest Mount Vernon mansions to the humblest West Baltimore rowhouses. Descriptions of structures and pointers to published pictures in the library's collection are indexed on cards in the Passano file, named for its creator, Eleanor Passano.

For the last 17 years, the job of reorganizing the image file has fallen to O'Neill, and in recognition of his work, the society announced Saturday that it will be rechristened, with his name joining Passano's.

"I was surprised," O'Neill said. "It's a nice thing to have, but I don't know I'll ever refer to it as the Passano-O'Neill file because I've been working with it so long as the Passano file."

O'Neill spoke as he set about helping Lawrence Ripley, 77, figure out whether his grandfather's house was once the residence of a brewer or a funeral home.

When she began building her file, Passano grouped it by family names, O'Neill said. But over time as residents changed, family ties became less helpful and few researchers turned to the file. Starting in 1995, O'Neill set about reorganizing it by block.

"Property research is a tricky business," O'Neill said, but with a bit of work, people should be able to piece together the history of their building back to at least 1880.

"Usually the best thing to do is start in the present day and work backward," he said.

Mike Bowman, 30, recently bought a house in Fells Prospect, or Upper Fells Point, and was trying to learn as much about it as he could. He had been working both backward and forward and said he has been able to work out some of its history before 1920 and after 1960.

"I'm here today to try to fill in the gap," Bowman said. "I'm just an obsessed hobbyist."

Bowman has been writing about his discoveries at the Castle Street house on a blog.

He found out that a previous resident was a fireman whose son was once arrested for having 10 bottles of beer on a Sunday. A sympathetic jury deadlocked on charges against the man accused of selling the beer, according to an old news report Bowman unearthed, and a judge advised prosecutors that they might want to consider potential jurors' feelings more carefully next time.

Bowman said he's proud of being able to piece together some of the history of his working-class street.

"You can really close your eyes and think of him coming home covered in sweat and ash," he said of the fireman.

At another table in the library, Donna Carter, 45, a lab technician, was poring over an old fire insurance map of East Fort Avenue and trying to work out when a house connected to her family was torn down.

Carter, who began digging into her family's past at her grandmother's feet as a teenager, said even little details, like whether a family rented or owned the home, can be revealing.

"If they rented, they didn't have a lot of money," she said. "If they owned, they were a little bit more established."

Bowman had done most of his research online, but the librarians at the historical society described an array of older offline sources. They include city directories, which listed the names and addresses of Baltimore residents and can be browsed by name and, after 1928, by street.

Chasing the past is a challenging task, the librarians said, but Dennis had measured words of support.

"We're happy to assist you with your homework," he added, "but we won't do it for you."

iduncan@baltsun.com

twitter.com/iduncan