Every seventh person in the world uses Google and other websites the company owns, a media report said.
The landmark figure in May revealed by ComScore shows an 8.4 percent rise year-on-year. Over one billion people among the world's current population of 6.93 billion use Google and its other websites.
Microsoft remained the second most popular destination with 905 million unique visitors in May, the Daily Telegraph reported.
This was up approximately 15 percent over the year, but Facebook rose by 30 percent to 714 million unique users, it said.
Yahoo, which was overtaken by Facebook in October, saw an 11 percent yearly rise to 689 million users.
A "global measurement panel" of two million users helps ComScore to compile its estimates, and the data is then refined with page-view data it receives from more than 90 of the 100 publishers of web content, the report said.
Google is one of the few publishers that does not contribute. The company declined to comment.
When ComScore first measured traffic, in 2006, Google had slightly fewer than 500 million unique users per month, with Microsoft taking the top spot with 539 million, the Telegraph said.
The addition of users to Gmail and Google has also been helped by the company's purchase of video site YouTube.
Users, however, spend more time on Facebook than Google; the social network's users browsed the site for 250 billion minutes in May, compared to Google's 200 billion, according to the newspaper.