The number amounts to one-seventh of the Earth's population.
Monday's milestone was mostly symbolic for Facebook, which boasts nearly 1.5 billion users who log in at least once a month. But CEO Mark Zuckerberg, who founded the network in his Harvard dorm room 11 years ago, reflected on the occasion with a post.
"`I'm so proud of our community for the progress we've made," he wrote. "Our community stands for giving every person a voice, for promoting understanding and for including everyone in the opportunities of our modern world."