From this article on allfacebook.com :
India is the world’s second most populous nation, with 1.22 billion people. According to Facebook’s advertising dashboard, 39.6 million people in India now have accounts on the social network. Facebook has been India’s leading social network since overtaking Orkut there in the summer of 2010. Yet the vast majority of India has yet to discover social media, let alone the Internet, as only ten percent of the country’s population has online access.
