What’s the fastest growing classified site out there? I’ll give you a hint – it’s one where you can post for free.

Web traffic tracking Hitwise recently reported on the growing dominance of Craigslist in the classified ad space. Here’s a chart showing the growth of the site’s market share in the past few years:

Put simply, more and more people are going there, including your next potential employees. It’s spreading geographically, too. The biggest segment of visitors is still in California (the site started in San Francisco) but the sharpest growth is happening in other parts of the country, specifically Texas, Florida and New York.

So what’s in it for HR? As I mentioned earlier, posting to Craigslist is free in most cities, and just 25 bucks a pop in others. That means your notice might be alongside a lot of garbage, which can hurt your chances of targeting the right people – but if it doesn’t work, you won’t be wasting any money.

It’s probably not the best place to find a higher-level manager, but for entry-level jobs and temporary or contract work, it seems to be worth the try. Have you had success advertising jobs on Craigslist? Tell us about it in the comments section.