The milestone follows the news earlier this year that global membership of the site, which focuses on linking people up because of their business connections, had crossed 50 million.
The company did not release any details about how many people are paying for premium membership.
While panic about job security may be one factor in LinkedIn's 2009 growth, the site's European managing director, Kevin Eyres, put a more positive spin on the achievement.
"It's not down to the range of features we offer, the speed at which we innovate, or the number of languages the site is available in. It's the members and the rich mix of expertise, experience, wisdom and the positive, collaborative attitude that they bring."
No matter what the situation with the job market in 2010, the site looks set for continued growth having signed partnerships recently with Twitter and Microsoft.
The Twitter deal means that members of both sites can now have their Twitter updates appear in their LinkedIn profiles.
Microsoft is planning to integrate Twitter in to the next release of its email programme Microsoft Outlook 2010.