LinkedIn has announced that it has finally reached a major milestone: 100 million users and counting.

The company, founded in December 2002 and launched in May 2003, reached profitability fairly soon, and its growth has been accelerating over the last few years. It took LinkedIn six years to reach 50 million users, but it only took a year and a half for the business social network to double that number. LinkedIn hit 85 million members in October 2010 and revealed that it had more than 90 million users when it filed to go public earlier this year. LinkedIn is now adding one new member per second.

To celebrate its new achievement, the LinkedIn team has released an infographic breaking down its growth and its overall membership. It comes with several interesting tidbits of information on who uses LinkedIn and even when they use it.

Here are some of the most intriguing stats from LinkedIn’s infographic:

• 56% of LinkedIn’s users are outside of the United States. LinkedIn is experiencing its fastest growth internationally.
• LinkedIn’s fastest-growing country is Brazil, with 428% growth year-over-year. Brazil is followed by Mexico, India and France.
• The height of LinkedIn activity happens during the workday, peaking at around noon. Mobile usage, on the other hand, typically peaks around 8:00 p.m.
• There are almost 1 million teachers on LinkedIn. 20% of the site’s users work in the service sector, while 9% work in finance and another 9% are in the high tech industry.

For most of its 7+ years of existence, LinkedIn has dominated its niche of social business users. The result is a valuation nearing $3 billion and 5.5 billion monthly pageviews. While it’s no Facebook, we bet most people would love to be in LinkedIn founder Reid Hoffman’s shoes right now.

We’ve included LinkedIn’s infographic for your viewing pleasure. Click on the image for a full-sized version.