“You probably thought you were the only one who loved Maud Hart Lovelace,” said Diane Gonzales, a social worker and the president of the Greater Chicago Chapter of the Betsy-Tacy Society. She smiled at scores of women who’d come from miles around, women of all ages and walks of life, and at little girls in pigtails and pinafores–or ponytails and jeans. They were at the Chicago Historical Society to celebrate what would have been Lovelace’s 101st birthday.

Behind Gonzales were two big poster boards. One was full of vintage black-and-white photos of the real people described in Lovelace’s ten novels. They were identified by both their fictional and real names, many of which rhymed. Also included was a picture of “Betsy”–Maud herself, with a big space between her teeth just as Betsy is described–and “Tacy,” whose name in real life was Bick. The other poster board was full of old pictures of landmarks in Mankato, Minnesota, places that showed up regularly and mostly undisguised in the fictional town of Deep Valley where the books are set.

There were little chocolate men that everyone could help themselves to, just like the ones Betsy and Tacy used to buy at Mrs. Chubbock’s store. And two women dressed up like cats did a cat dance, just like Betsy and Tacy used to do. There were Betsy-Tacy souvenirs. There was birthday cake.

Lovelace fans were transfixed by a few minutes’ footage on loan from the Minnesota Historical Society in which Lovelace describes how life in Mankato was so happy and how it so influenced her successful writing career. Then a middle-aged newspaper columnist from New Jersey got up and rambled on about the long correspondence she had with Lovelace and about the few occasions when they met. She said she felt like Lovelace’s protegee, and it helped her in her writing career immensely. But she was sorry she threw most of the letters away during a time in her life when she “wasn’t thinking too clearly.”

Two grown-up sisters walked by with big dazed smiles. Sharla Whalen of Naperville, Lovelace’s biographer, explained that the sisters’ mother–whose name is Betsy and who was a big Betsy-Tacy fan while growing up–married a guy named Joe (their father) just like Betsy did in the tenth book, Betsy’s Wedding. “The fact that his name was Joe really influenced her decision to marry him,” said Whalen, who wrote to Lovelace when she was 14 and offered to write her biography, “but she never wrote back.”

Lovelace was living in New York with her husband, Delos, and her young daughter Merian when she decided to memorialize her childhood and adolescence in Mankato in a series of novels for girls. She published the first one, Betsy-Tacy, in 1940. The hyphen between the names bespoke the inseparability of the two girls, who met in Deep Valley at the age of five when Tacy’s big Irish family moved to town.

These books caught on. And stayed popular. And are now being republished for a new generation of readers. According to Whalen, Betsy-Tacy fans include Bette Midler, Judy Blume, and Anna Quindlen. “The books were a lot more real than Trixie Belden and Cherry Ames books,” said Melanie Rigney, an editor at Advertising Age. As a child she borrowed the Betsy-Tacy books from a bookmobile in Sioux Falls, South Dakota. “I had no idea they really took place in Mankato, which was just 200 miles away.”

Rigney still reads the books regularly. In 1987 she came across a card in one she’d checked out from the library. It was from Whalen asking readers if they had any information about Lovelace for her biography. (“She always put the cards on page 100,” said Rigney.) That’s how many of the Betsy-Tacy lovers began finding each other; and in 1990 the society was formed.

“Trixie Belden may have solved mysteries, but she never quite developed,” said Rigney. “She never had self-doubts. Betsy always worried that she wasn’t pretty or whether she’d get a boyfriend. She went to parties and blew off an essay-writing contest. She had fun and was frivolous, but then she’d worry that her writing would go away forever. Trixie Belden didn’t think like that. Betsy was like someone you would really know.”

Rigney said Betsy-Tacy devotees have gone through the books, printing up the lyrics to the songs mentioned and compiling recipes for all the foods mentioned. They collect the plants named. They go on vigils in the streets of Mankato. They advertise to find each other. “You don’t find people doing this kind of thing for the Humane Society” said Rigney.

Whalen, the biographer, who has three small children, traveled around Europe to all the places Betsy saw in Betsy and the Great World. She’s traveled the country sorting out the fiction from the reality in the Lovelace saga, discovering all sorts of obscure facts about her world–the real color of a character’s wallpaper, for instance. She claims that some of the characters are composites of people in Mankato and has uncovered who they were: the person with a red car, the one with an olive complexion, the wealthy one. She knows what happened to all the characters in real life, where they lived, what they did, when they died, who and where their descendants are. Betsy’s fictional sister was a good singer; Lovelace’s real-life sister became an opera star, and wept after every performance out of exhaustion and emotion.

“There really was a Marco in her life,” said Whalen, referring to a dashing character who swept Betsy off her feet. “His real name was Paul. I don’t know why she didn’t marry him. Maybe he didn’t share her interest in writing like Delos did. But he followed her back to Mankato [from a European tour], and her sister wondered how she resisted marrying him.”

“We can never get enough of Sharla,” said Gonzales, the chapter president.

Whalen went on. “Whenever I’m upset at night and up with a stomachache, I reread Heaven to Betsy or Betsy’s Wedding. Although the novelty is starting to wear off.”