Foursquare, the location-based social-networking service, registered its 100 millionth 'check-in' on Monday evening.

The check-in marks another landmark for the service, which has seen rapid growth in recent months. On June 23 the company said it was growing at the rate of 100,000 users every 10 days - a rate that would put its current userbase at more than 2 million people, assuming growth held steady over the past month.

Foursquare connects users with their friends in the real world by allowing them to register their current location via check-ins. The check-ins are shared with friends and often with strangers via social-networking services like Twitter. Typically accessed through a GPS-equipped mobile phone, users can register new locations if their current locale is not already in the database of hundreds of thousands of places.

The company didn't detail where the 100 millionth check-in took place.