Cook County Sheriff Thomas Dart sued Craigslist in a Chicago federal court, calling the site “the single largest source of prostitution in the nation.”

Dart’s department has made dozens of arrests of prostitutes and their customers who use Craigslist to set up liaisons. In June, Dart’s deputies busted 76 in a prostitution sting, where undercover officers posed as johns.

The sheriff is trying to get the court to order Craigslist to shut down the Erotic Services section of its site. “Missing children, runaways, abused women and women trafficked in from foreign countries are routinely forced to have sex with strangers because they’re being pimped on Craigslist,” Dart accused.

In a press release, Dart cited ads that allegedly solicit youngsters into a life of prostitution: ” Teens for cash … $100 quickie” and “Are you looking to make some good money in this tough economy? Minimum pay is $25 per hour … performing duties specified in the Naughty Nannies handbook.” Here’s a link to the 28-page complaint (PDF).

More from the Chicago Tribune. No official comment from Craigslist. In late 2008, Craigslist pledged to crack down on prostitution ads as part of an agreement with several states attorneys general. The crackdown required erotic-service posters to pay a small charge via credit card, so as to create a paper trail for prosecutors.

At the time, we pointed out that prostitutes had already found a loophole by posting for free in Personals and mentioning their hourly rates.

It’s unlikely a court would attempt to compel Craigslist to remove any part of its service. U.S. Web sites enjoy quite a bit of latitude under federal electronic communications law. (And Craigslist is no stranger to the U.S. District Court in Chicago. Two years ago, a group of lawyers tried unsucessfully to hold Craigslist accountable for violation of the Fair Housing Act for accepting ads that sought to exclude renters by race and gender.)

Dart’s suit is more cage-rattling than anything. But it does beg the question of Craigslist: C’mon guys. Isn’t enough, enough?