Trinity Mirror made the milestone announcement in a release today.
Of those unique visitors, 49 per cent used a mobile or tablet device to access the site while 51 per cent used a desktop computer.
Martin Belam, UsVsTh3m's project lead, told last Friday's news:rewired digital journalism conference that unique visitors to the site had reached 750,000 by its second month, of which one percent was from search. "It's all about social," he said.
UsVsTh3m, which has almost 10,000 followers on Twitter, creates original articles, posts and interactive "toys", alongside curated content from around the web, aimed at a young, social, mobile audience.
"Our toys are our USP," Belam added
The most popular of such toys is 'Down with the kids', an interactive quiz on popular culture, which has so far been played by 470,000 people, according to a press release accompanying the announcement.
Another game, built when the US and UK were considering military action against Syria following the chemical weapons attack on the Ghouta agricultural belt around Damascus on August 21, asked users to pinpoint Damascus on a map.
This received 266,000 users, some of whom were traced to the US Department of Defense and the Houses of Parliament.
Malcolm Coles, digital product director at Trinity Mirror said in today's press release: "UsVsTh3m only launched at the end of May. It's an amazing achievement by the team to have grown so quickly and shows the importance of experimentation for publishers."