Rachel Rolerson-Smith didn’t like her friends’ dark plans for her upcoming 50th birthday.

So, the Isleboro resident thwarted their scheme by creating a chapter of the Red Hat Society, a national group of women devoted to celebrating life after 50.

“They were going to dress in black and have black balloons, but I said, ‘No way, I’m celebrating this,'” Rolerson-Smith said Sunday. “My sister-in-law suggested I join the Red Hat Society and go out and have some fun, and I have.”

Sue Ellen Cooper, founder and Exalted Queen Mother of the Red Hat Society, would approve. She inadvertently founded the group in 1997 when she bought a red hat for herself as a 50th birthday gift, then began giving red hats to her friends as they reached that milestone.

Cooper has said she was inspired by the poem “Warning,” by the English poet Jenny Joseph, now in her 70s. “When I am an old woman I shall wear purple/With a red hat which doesn’t go and doesn’t suit me,” wrote Joseph. “And I shall spend my pension on brandy and summer gloves/And satin sandals … ”

The idea spread through Cooper’s friends in Southern California, then snowballed via the Internet. Today, there are 20,000 chapters and membership is approaching 500,000. New chapters are formed daily, sparked by the release this month of Cooper’s paperback book “The Red Hat Society: Fun and Friendship After Fifty.”

Members of the Classy Ladies chapter in Waterville met Sunday at Borders in Bangor to celebrate the book’s publication. Six women dressed as if they were headed for tea at Buckingham Palace created a bit of a stir amidst the patrons clad mostly in flannel and denim.

Fran King, Queen Mother – in Red Hat lingo, the person who keeps chapters organized – helped found the group six months ago. A retired executive secretary whose five grown children all live out-of-state, she said the goal is to have fun.

“If we don’t have fun,” she said, “we don’t do it.”

The group now has 18 members and meets once a month to plan an activity or outing. In June, they’re going to Boston to see the hit musical “Menopause.”

“When I put this hat on and go out, I feel young and happy and beautiful,” King said, pulling on her long, red satin gloves.

There are few rules in the Red Hat Society and those that have been established are flexible. One, however, is ironclad: Members don’t don red and purple until they pass the half-century mark. Before that, they must wear the less intense sister colors of pink and lavender and are mere princesses.

Although she won’t turn 50 until Sept. 3, Rolerson-Smith, who with her three business partners and fellow Red Hatters owns the product brokerage firm Market America, has purchased a red hat for the occasion. Already, her month-old Red Hat Society chapter, the DownEast Dames, has six members, including a summer resident from St. Louis.

“On our first outing, we went down to the Bees’ Knees [in Islesboro] and did makeovers with our pink hats on,” Rolerson-Smith said. “People were taken by surprised. ‘What are you doing?’ they asked. We said, ‘We’re just celebrating life and having fun.'”

That is, after all, what the Red Hat Society is all about.

For more information on the Red Hat Society, visit www.redhatsociety.com.