The six-member Board of Aldermen made Internet harassment a misdemeanor, punishable by up to a $500 ( EUR 338) fine and 90 days in jail. Mayor Pam Fogarty said the city had proposed the measure after learning about Megan Meier's death.
"It is our hope that by supporting one of our own in Dardenne Prairie, we can do our part to ensure this type of harassing behavior never happens again, anywhere," Fogarty said, adding, "after all, harassment is harassment regardless of the mechanism or tool."
Several dozen people broke into applause after the measure was passed.
Authorities have said they could not find a crime to charge anyone with in the case of Meier, who thought she had met a good-looking 16-year-old boy on the social networking site MySpace last year. But he began sending her mean messages and others joined in, her family said, and then he abruptly ended their friendship.
Megan hanged herself within minutes of receiving the last messages on Oct. 16, 2006, and died the next day.
Megan's parents, Ron and Tina Meier, learned about six weeks after Megan's death that the boy, Josh Evans, was not real. The boy was created by a mother down the street who wanted to know what Megan was saying about her own daughter, who had had a falling out with Megan.
Her father said he found a message from Josh, which he said law enforcement authorities have not been able to retrieve. It told the girl she was a bad person and the world would be better without her, he has said.
The four-page measure defines both harassment and cyber-harassment, essentially making it illegal to engage in a pattern of conduct that would cause a reasonable person to suffer "substantial emotional distress," or for an adult to contact a child under 18 in a communication causing a reasonable parent to fear for the child's well-being.
City attorney John Young said constitutionally protected activity would be exempt. The measure would apply when one of the people communicating was in Dardenne Prairie.
During a break in the meeting, Fogarty embraced Megan's mother with tears in her eyes. She said she was sorry there had not been a law previously in place to prosecute Megan's harassers.
Tina Meier said she was thrilled that the city had passed the new measure.
"This is not a stopping point," she said. "We're not done."
City officials also passed a resolution encouraging state and federal officials to outlaw cyber-harassment and cyber-stalking. A state lawmaker has questioned how state law could be altered without running afoul of First Amendment constitutional issues guaranteeing freedom of speech.