• by Wendy Davis , Staff Writer @wendyndavis, October 21, 2009

A federal judge in Illinois has dismissed a lawsuit by Cook County sheriff Thomas Dart accusing Craigslist of creating a public nuisance by allegedly running prostitution ads.

U.S. District Court Judge John Grady in Illinois ruled Tuesday that the federal Communications Decency Act protects Craigslist from liability for unlawful ads submitted by users.

"Sheriff Dart may continue to use Craigslist's website to identify and pursue individuals who post allegedly unlawful content," Grady wrote. "But he cannot sue Craigslist for their conduct."

Dart sued the listings site in March, arguing that it "knowingly and intentionally facilitates prostitution" through its erotic services ads. Craigslist later replaced that section with monitored adult ad listings, but Dart argued that the new section still included ads for prostitution.

Craigslist says that the adult ad listings are meant for racy but lawful services, like erotic dancing.

Among Dart's arguments about why Craigslist should be liable, he alleged that the site was costing the county money because police officers monitored Craigslist to find and arrest suspected prostitutes. Dart mentioned one recent operation that resulted in 156 arrests, at a cost to the county of $105,000.

But, as observers pointed out, arresting prostitutes would likely have cost the county even more money if the suspects hadn't advertised online.

Grady's decision to dismiss the case isn't a huge surprise, given that a federal appellate court in Chicago has already ruled that Craigslist can't be sued for illegal housing ads.

Still, that hasn't stopped various state attorneys general from continuing to try to force Craigslist to shutter its listings. South Carolina Attorney General Henry McMaster threatened to haul Craigslist executives into court on criminal charges, prompting the site to file a lawsuit seeking an injunction against him. McMaster agreed to a temporary injunction, but says the court should not issue a permanent one. That case is still pending in Charleston, S.C. federal district court.