Compete has just released their July numbers, and here’s the latest: after growing by at least a few percent during each of the last several months, Compete says traffic to all Facebook domains (including the main Facebook.com site and all Facebook Connect integrations) held steady in July at 122.7 million US uniques.

However, Compete’s subdomain breakdown for July is somewhat confusing. Traffic to the main Facebook.com site was up 27% in July to 117 million US unique visitors which, if correct, would be astounding growth at triple the rate of previous months. However, Compete also reports that traffic to Facebook Connect sites was down 40% in July to 42.6 million US uniques which, if correct, would be an astounding decline after 10 months of consecutive growth. We can think of two possibilities: either Compete is miscategorizing big chunks of data, or some sites have moved Facebook Connect related code to the main www.facebook.com domain. While this makes Compete’s July data feel less reliable, we’re assuming the overall traffic numbers to all Facebook domains are still relatively accurate.

Facebook, MySpace, and Twitter US Uniques – Last 12 Months

By contrast, Facebook’s advertiser tools reported 10% month over month audience growth in the US during July, up to 76.6 million from 69.4 million in June. That 10% clip was faster than both of the previous two months.

In addition, acording to Compete, traffic to MySpace and Twitter domains were flat during July too. MySpace actually declined 2% to 59.6 million uniques, while Twitter traffic grew by 1% to 23.2 million uniques.