Liberal political news site The Huffington Post first integrated Facebook Connect last January, then it launched a new part of the site in mid-August, called Social News, that let users share and comment on news stories with their Facebook friends. Some results are, and they seem pretty good.

First, to try to gauge the overall effect of Connect on HuffPo’s site, here’s some general numbers. The news site’s traffic doubled in the past year to 6.83 million unique visitors last month, according to comScore; Nielsen, meanwhile, reported that the site grew 26% over the same period to reach 9.47 million.

Now, for Facebook numbers. HuffPo told PaidContent yesterday that Facebook referrals added up to 3.5 million visits in September, up 190% from July and up 500% in January.

Given that HuffPo’s Facebook numbers are self-reported, we don’t know exactly how they fit in with comScore’s or Nielsen’s numbers. But it told PaidContent that Google Analytics shows it reaching 27 million monthly uniques for September — so, Connect helped to generate nearly 13% of the site’s September total traffic?

Meanwhile, the number of comments grew from 1.7 million to 2.2 million in July (we assume that means comments per month). 15% of all comments are now coming from Facebook, according to the article.

As some large newspapers have lost readers, the fact that HuffPo was able to grow — especially in a non-election year — seems at least partly attributable to Connect.