MADISON, Wis. — Annie Laurie Gaylor clicked through a flurry of e-mail messages warning her to repent or she would burn in hell.

“Herod,” one messenger called her.

Ms. Gaylor leaned back and sipped from a cup of tea, unfazed and even a bit surprised at the relative tameness of the attacks. Fresh from her latest godless triumph, she had expected more vitriol.

“It used to be a lot worse,” said Ms. Gaylor, 54, an atheist whose organization, the Freedom From Religion Foundation, recently won a suit in federal court here that declared the National Day of Prayer to be a violation of the First Amendment. “Things are changing. Society is becoming more secularized. It’s becoming acceptable to be atheist and agnostic. And there are more of us.”

The nation’s population continues to show signs of becoming less religious, according to the American Religious Identification Survey. The number of people in 2008 calling themselves atheist or agnostic, or stating no religious preference, is an estimated 15 percent, nearly double the percentage in the early 1990s. Around the country, nonbeliever clubs are springing up on college campuses.