Mr. McLenahan served as the commission's executive director from 1968 to 1993. He started early in the preservation movement, when the concept of saving old buildings wasn't always popular.
"In those days, preservation wasn't quite thought of the same way it is today," said John Hern who served as the deputy director. "It was kind of depressing in the beginning."
Mr. McLenahan, 71, died of complications from emphysema on Saturday, July 16, in his Hyde Park home, said his longtime friend Mary Borecki.
Born in Berwyn, Mr. McLenahan spent most of his adult life in Hyde Park, said Borecki, who met him in the neighborhood in the late 1970s.
One of his strengths on the commission was his skill at communications, said Ozzie Badal, who worked for the city's urban planning department.
"He was always very thoughtful and clearly investigated all kinds of things necessary for any projects that came before the commission to ascertain the facts," she said. "He had a good sense of what landmarks should be."
In 1971 the Chicago Stock Exchange Building was demolished, to the dismay of Mr. McLenahan and other preservationists, said Susan Benjamin, who worked as Mr. McLenahan's assistant on the commission. Architects Louis Sullivan and Dankmar Adler designed the building, and it was built in 1893-94.
"Preservationists subsequently recognized that losing the Chicago Stock Exchange Building was an enormous loss to the city," Benjamin said. "It was (Mr. McLenahan's) job to execute the policy of the commission and the city. … Sometimes that was challenging and difficult."
His love of architecture ran deep and was reflected in his homes, which he remodeled and decorated himself, Borecki said.
"He was a very creative person," she said. "He had a real sense of how things were put together."
Mr. McLenahan traveled widely through Europe, loved art and independent film and for many years had a subscription to the Joffrey Ballet.
He truly took advantage of "the whole wonderful gamut of things we have available to us here in Chicago," Borecki said.
"He was a city person," she said. "He was not going to be out in a small town."
Friends also remember Mr. McLenahan as a fabulous cook.
Later in his life, Mr. McLenahan worked for Hyde Park's Century 21 as a salesman, sales manager and eventually advertising manager.
Even when his health was failing, he would call the firm's owner, Jeanne Spurlock, five times a week to discuss work, Spurlock said. He was preparing an ad when he became gravely ill, Spurlock said.
Mr. McLenahan was a "fabulous" salesman who truly cared for his clients, she said.
"He knew every building in Hyde Park," Spurlock added. "He was just a wealth of information."
Mr. McLenahan is survived by his brother, Tom.
There will be no services.