In contrast, 78 percent of the developed world's population is online, data in the 2014 State of Connectivity report by Facebook's Internet.org project published on Tuesday shows.
The report said that 37.9 percent of the global population use the Internet once a year.
The rate of adoption of the Internet is currently slowing, decreasing for the fourth consecutive year since 2010, according to the study.
The report said that by early 2015, three billion people are estimated to be online, but due to the slowing rate of Internet adoption, this number will struggle to reach four billion by 2019.
Infrastructure, affordability and relevance are named as the three barriers to Internet access around the world.
The study also asserts that the Internet is an economic enabler, the growing use of which will exert a great effect on the global economy. The company noted that the Internet increases opportunities for everyone, and that is why it was important to eliminate obstacles to its expansion.
Facebook launched its Internet.org project in partnership with major mobile phone companies in 2013. The project aims to provide affordable Internet access globally, especially in developing nations.
