[The data in this article is excerpted from the Facebook Global Demographics Report, part of our research and data subscription service at Inside Facebook Gold.]

The US Facebook-using population grew by 4.73 million over the course of September, reaching 138.6 million monthly active users from 133.9 million in August. The data, derived from Facebook’s advertising tool, showed a growth slowdown earlier in the summer. Whether it was college students coming back to school, or fewer people working and playing indoors, or other reasons, the surge helped make the month Facebook’s highest US count to date.

We normally break out the demographic data in more detail, but the sex and age cohorts showed odd results that suggest the possibility of a bug, or noise, even though the overall numbers were typical. For this reason, we’ve omitted these breakdowns in the chart below.

You can take a full look at the data in our latest demographics report, coming through Inside Facebook Gold in the next couple of weeks. In the meantime, here’s a historical view of total US traffic over the last 12 months, as we’ve recorded it.

As you can see, there continue to be more women on the site than men, with the disparity increasing slightly in September, now reaching 56.3%. Note that the “Total” line represents the sum of women and men, but appears slightly lower than the “Overall” line. The reason is that the latter measure includes users who have not designated their gender.