According to a survey released on Thursday, close to 694 million people worldwide over age 15 use the Internet.
The report by research firm comScore Networks claims to be "the first true estimate of global online audience size and behavior" using consistent methodology.
The estimate was based on a survey of major markets including China and India.
"Today, the online audience in the US represents less than a quarter of Internet users across the globe, versus 10 years ago when it accounted for two-thirds of the global audience," said Peter Daboll, president and chief executive of comScore Media Metrix.
According to the report, the United States still had the single largest Internet audience, of 152 million users, followed by China with 72 million.