Facebook founder and CEO Mark Zuckerberg appeared on the TODAY show in an exclusive interview with Matt Lauer show earlier this morning to announce a “historic milestone” Faceboook now has one billion users.

In the United States, almost everyone who wants to be on Facebook already has an account. Growth over the past year in the US is just 9%, not a big increase. Abroad, however, Facebook has been making huge gains in terms of number of users.

The Biggest Facebook Growth is Happening Abroad

This past year, Facebook growth in Japan exploded, with a 507% increase in users. That by far is the biggest percentage growth, though other countries have continued to expand their Facebook usage as of late. Three of the top 20 counties doubled their numbers of Facebook users in the past year, including Brazil (which is now #2, behind the US, in total number of users), Thailand, and Egypt. India saw nearly 50% growth, though it dropped to #3, bringing its numbers up to 56 millons Facebook accounts.

Around 32% of the world’s population is online, or around 2.26 billion people. Facebook is clearly starting to reach a critical mass, and it’s future growth may actually be limited by how many new homes the Internet can reach in the coming years. As well, Facebook is still blocked in China, denying it access to more than a billion people.

A billion people on Facebook is a staggering number, thats just about 44% of everyone who’s online. Other online services may have tons of users, but none of them actually come close. Twitter boasts 500 million users, and Gmail claims 425 million users.

While all of these services suffer a certain difficulty in reporting a true number of unique users (some people have more than one account, or abandon their accounts), one thing is true: people are engaging with Internet services, especially social ones, in huge numbers right now.

If you want to see the complete growth numbers for Facebook broken down for each of the top 20 countries, scroll to the end of the article—we’ve got the full list of numbers of users by country, current as of last month.

Facebook’s Biggest Challenges

One of the big challenges Facebook has faced as of late is in mobile. While their pickup on Instagram meant they added some serious talent to their mobile team, it was only in late August that they finally got it together on iOS and released a decent version of the app. But it’s much improved today—the new app is much faster and smoother, and I actually use it daily now. The next challenge? How can Facebook monetize the mobile audience. With an estimated 500 million or so people accessing Facebook on mobile devices, there is a huge new market segment waiting to be capitalized on. How will Facebook tackle that problem in the coming years?

In an interview with TechCrunch founder Michael Arrington, Zuckerberg said that “I am really optimistic about our mobile monetization strategy.” Optimism is one thing, but what will that strategy be? The recently launched mobile ads are one thing that seem to be working well, according to Zuckerberg: “Those mobile ads perform better than the regular column ads on desktops.” That’s a start, but time will tell if Facebook has more up it’s sleeve than just a new ad format.

Want to know more about how Facebook is focusing on mobile? Read my recent article about the future of social media on the Networking Exchange blog to find out!

New Facebook Features

There have been some cool additions to Facebook recently that are worth pointing out. The first is that people in the US can now take advantage of a feature that brands and businesses have had for a while: promoted posts. Facebook is currently testing promoted posts for individuals, which could be a great way for entrepreneurs and small businesses professionals who have large personal followings but are struggling to build their brand’s pages to get additional traffic while they hammer out a social media strategy.

Another helpful change to facebook is that they’ve updated their Help Center and Support Dashboard recently to make them easier to use. As a notoriously complicated service on the backend, with tons of hard-to-understand privacy features, this is a welcome change for Facebook and will hopefully help people make better decisions about privacy settings and how they use the service.

Top 20 Countries by Number of Facebook Users

(Source: Facebook’s Estimated Reach Indicator / Forbes)

NO.	NATION	SEPT 30, 2012	SEPT 30, 2011	GROWTH RATE
1	United States	166,022,260	151,419,860	9.64%
2	Brazil	58,483,180	29,301,860	99.59%
3	India	56,675,740	37,377,600	51.63%
4	Indonesia	43,814,560	40,515,180	8.14%
5	United Kingdom	42,071,100	30,393,440	38.42%
6	Mexico	38,538,760	29,802,980	29.31%
7	Turkey	32,194,820	30,636,800	5.09%
8	Philippines	29,878,240	26,116,980	14.40%
9	France	25,236,960	23,190,260	8.83%
10	Germany	24,596,460	21,461,340	14.61%
11	Italy	22,424,380	20,525,400	9.25%
12	Argentina	20,066,480	17,089,240	17.42%
13	Canada	18,082,780	16,856,000	7.28%
14	Colombia	17,322,020	12,675,160	36.66%
15	Spain	17,018,440	15,142,360	12.39%
16	Thailand	16,834,140	8,421,780	99.89%
17	Japan	15,506,260	2,553,660	507.22%
18	Malaysia	13,063,600	10,138,760	28.85%
19	Taiwan	12,937,760	9,999,260	29.39%
20	Egypt	11,770,720	5,651,080	108.29%