While metrics from other analytics firms say Facebook’s US growth slowed in July, new data just in from comScore actually tells the opposite story. According to comScore, Facebook’s traffic to its main site grew by nearly 14% month over month in July to over 87.7 million US uniques – the highest monthly growth rate Facebook has experienced in the last year. Here’s how the numbers break down:

As you can see, Facebook’s US traffic grew substantially in July – blowing past 80 million monthly uniques all the way to 87.7 million. MySpace stayed roughly flat at 68.3 million uniques, and Twitter continued a steady 5% growth rate to 21.2 million uniques after exploding earlier this year.

The story here, though, is Facebook hitting an all-time high growth rate in the US, according to comScore. It now seems that the redesign earlier this year hasn’t been “disastrous” as some people have claimed – while Facebook is still working on improving the “highlights” section of the home page and perhaps re-integrating it with the real time stream, Facebook’s American audience has continued to expand across the demographic board. (Note, however, that very rapid growth could be masking any retention issues associated with the redesign.)

To zoom in on the social networking growth numbers in more detail, click the chart below:

In the last year, Facebook has grown from half of MySpace’s audience in the US to now being the clear leader in comScore’s “Social Networking” category – and doesn’t show any signs of slowing down yet. Meanwhile, Twitter is sustaining a substantial US audience, but unlike Facebook, Twitter doesn’t require users to have active accounts to view the site. comScore says all reported numbers count only traffic to Facebook’s main site – not Facebook Connect widgets or any other distributed content.

Source: comScore Media Metrix