Now that Zynga‘s FarmVille game has proven to be a smash hit on Facebook, the company is launching the game on Microsoft’s MSN Games portal.

That’s a big deal because it shows that Zynga is diversifying away from the social network that made its games some of the most popular in the world. FarmVille has grown to more than 76 million monthly active users on Facebook since its launch in June of last year. That kind of growth is unprecedented for a game.

Late last year, Zynga started, a stand-alone web site, to expand its reach. And now the launch on MSN Games could help Zynga reach millions more. MSN Games draws tens of millions of visitors a month.

“Social gaming has gone mainstream,” said Mike Verdu, senior vice president of games at Zynga. “People love to connect with their friends through our games, which are broadly accessible and have universal themes. Bringing FarmVille to a major site like MSN Games is a great way to expand the reach of social games and is a logical next step in how we deliver them to consumers.”

MSN Games already has more than 1,000 games.

Check out our GamesBeat@GDC conference in San Francisco at the Game Developers Conference on March 10. One of the speakers will be Brian Reynolds, chief designer at Zynga.