East 84th Street, as It Was and as It Is Damon Winter/The New York Times; Collection of Lillian Jacobs CONSTANCY Lillian Jacobs, now 102, moved to East 84th Street at 2. Her parents ran a candy store, right, in the building where they lived. Bottom, Ms. Jacobs's signature on a library ledger from 1916. WHEN Lillian Jacobs was 2, in 1911 or "12, her family moved from the Lower East Side into a tenement building on East 84th Street, just off York Avenue, then known as Avenue A. Her parents ran a candy store on the building's ground floor, catering to the newly arrived immigrants from Germany, Hungary, Austria and Ireland. People came and went over the years; apartment houses were built and tradesmen's shops disappeared, along with the family candy store. But the character of the area, and specifically this part of East 84th Street, has largely remained the same. The brownstones, built at the turn of the 20th century and flanked by trees planted in more recent years, have stayed true to the block. So has Ms. Jacobs. Since arriving on East 84th Street, Ms. Jacobs, who is now 102, has moved to four different addresses, but always stayed on the street; her five homes have all been within 1,200 feet of one another. "I don't know why," she said last fall in her sunlit apartment on the 17th floor of a building near First Avenue, where she and her husband, George, moved two decades ago. But it seemed to be destined that I stay on East 84th. Ms. Jacobs is already a demographic rarity: she was one of 2,126 city residents 100 and over recorded in the 2010 census. But even though very few New Yorkers can claim a century spent in essentially one place, the notion of maintaining roots on a street is not entirely uncommon, said Andrew A. Beveridge, a Queens College sociologist. A decade ago, Professor Beveridge recalled, one of his students interviewed a man of about 100 who had lived his entire life in the same house in Richmond Hill, Queens. Bruce D. Haynes, a sociologist at the University of California, Davis, who grew up in Harlem, said that his own father spent the better part of 65 years in a house on Convent Avenue in its Sugar Hill section, until his death in 1995. "I'd argue that these are the people who make the city what it is," said Professor Haynes, whose grandfather, George Edmund Haynes, was a co-founder of the National Urban League. They are the character of the city. Indeed, Ms. Jacobs's stretch of East 84th Street, a tree-lined residential area near the heart of Yorkville, once the city's thriving German community in the northeastern quarter of the Upper East Side, has a number of longtimers. Bettymae F. Cronheim, 92, a teacher retired from the Ethical Culture School, has lived for more than 60 years in a second-floor apartment in a five-story building at No. 510; she recalled taking her children to visit the candy store run by Ms. Jacobs's parents. Henry J. Stern, 76, the former city parks commissioner, has lived for 50 years in a third-floor apartment in the same building. When he first arrived in 1961, he said, a young boy, Stephen Winer, lived down the hall. Mr. Winer, now 58, returned to the building after college, has spent much of his adult life there, and again, lives down the hall from Mr. Stern. "I've seen him grow," Mr. Stern said. I've seen him go to college, get married. He's seen me get married, have kids. "The life cycle is repeated in front of your neighbors," Mr. Stern added. A 1997 newsletter of the East 84th Street Neighborhood Association noted that the Upper East Side was mostly farmland and country estates in the late 1700s and early 1800s; it was after the Second and Third Avenue elevated subway lines opened in the late 1800s that brownstones and tenement buildings began to be built in Yorkville. It was into one of these tenements that Ms. Jacobs and her parents, Louis and Anna Rosenblatt, moved, in 1911 or "12, from another tenement in Lower Manhattan. Ms. Jacobs said her parents had always told her they arrived when she was 2. The 1913 edition of the Trow's directory for Manhattan, lists Louis Rosenblatt - "variety 500 ½ E84th" - as of August 1912. Her father and mother, immigrant Jews from Austria and Russia, respectively, spoke little English at first, Ms. Jacobs said. Her father had been educated in Europe, but her mother, who had worked in a clothing factory in Lower Manhattan, signed her name with an "X." At first, the family lived in two rooms behind the candy store, which also sold toys, cigars, newspapers and comic books. Her mother created window displays involving toy soldiers, dolls, tea sets and the like. "People began to come from blocks all over," Ms. Jacobs recalled. The family later moved to an apartment above the shop; Ms. Jacobs described the building as "a real tenement house."