We’ve been keeping track of Facebook’s self-reported demographic statistics on the US market for a while now, and here’s the latest update for November 2, 2009. While Facebook says these stats, provided to advertisers, are not necessarily real time, they do give us a sense of how Facebook is growing.

On the whole, Facebook’s US audience grew by 6.8% in October to 94.2 million uniques (compare to latest data from Quantcast, Compete, and comScore). Here’s how Facebook’s gender and age numbers break down as of today:

(Note: about 5% of users do not report either gender or age, and are not included in this chart.)

Where did the growth come from? Primarily from younger audiences. Males 18-25 led Facebook’s demographic categories this month, adding nearly 1 million monthly active users to over 12 million. Females 18-25 also increased in number by nearly 1 million last month. In addition, women 35-44 showed strong growth, while increases in males 35-44 were lower.

While Facebook is still growing most quickly percentage-wise amongst users over 45 – an interesting demographic trend that started earlier this year – the growth rate amongst users under 18 is also picking up. Interestingly, the growth rate of males 13-35 is faster than females, closing the overall gender gap on Facebook somewhat. Women still represent 57% of the overall Facebook audience.

Overall, 48% of Facebook users in the US today are over 35, and nearly 20% of all US Facebook users are over 45. That’s a good sign for Facebook’s brand advertising business, which has brought 83 of the top 100 ad spenders on board, according to VP of Global Sales Mike Murphy.