The milestone was announced Wednesday at a splashy event in Santa Monica that was aimed at advertisers and featured performances from some of the website's biggest stars, such as the bands CDZA and Monsters Calling Home. It marks another step in YouTube's evolution from a quirky startup launched in 2005 to one of the most influential forces in today's media landscape.
YouTube crossed the 1 billion threshold five months after Facebook Inc. said its online social network had reached that figure for the first time. YouTube first hit 800 million monthly visitors in October 2011.
The vast audience has given YouTube's owner, Google Inc., another lucrative channel for selling online ads beyond its dominant Internet search engine.
Google bought YouTube for $1.76 billion in 2006 when the video site had an estimated 50 million users worldwide.
Since late 2011, YouTube has refocused its site to prioritize watching along distinct channels of its creators. Such channels were seen as better allowing advertisers to focus on certain genres of content like beauty or music.
In 2012, it seeded 96 channels with around $100 million in funding to help them accelerate that growth, often partnering with big-name Hollywood producers and directors that had made it big in movies or TV but not on the Internet, including "CSI" creator Anthony Zuiker. Later, YouTube vowed to spend another $200 million marketing the channels to boost viewers.
But Wednesday's event focused largely on those who had succeeded on YouTube before the channel-funding strategy was in place, such as Michelle Phan, a YouTuber who has been giving viewers makeup tips since 2006.
Robert Kyncl, vice-president and global head of content partnerships, acknowledged to reporters after the event that the channel funding strategy had not worked as well as hoped.
When asked if the channel funding investment had paid off, Kyncl said, "Every year we reserve the right to get smarter."
He said that while YouTube was committed to continuing to invest in content, he said more of such investment in the future would go to those channels that had already proven they can be successful at building an audience on their own.
"What we're looking for is the acceleration of those who are figuring out how to retail their content," he said.
AP Business Writer Michael Liedtke in San Francisco contributed to this report.