Geolocation check-in network Foursquare is edging closer to a new milestone — 7 million users. The seven millionth ID has been snapped up by a user in Romania, meaning that Foursquare is close to grabbing 7 million members. However, the number of user IDs does not directly correspond to the number of users on the service and, as such, user number 7 million, whomever that may be, has yet to join.

Our own Chris Credendino (an early adopter of Foursquare) tweeted back and forth with Foursquare CEO Dennis Crowley over the accuracy of user IDs a few weeks back. As a result, we know that the number of users is at least 137,331 fewer than the current user ID figure indicates.

While a new Foursquare user will see that their ID number is greater than 7,000,000, there aren’t quite 7 million users yet. However, with Crowley recently confirming that Foursquare has more than 6.5 million users and is adding more than 25,000 users per day, the service will hit the 7 million milestone very soon.

Since its launch just under two years ago, Foursquare has seen steady growth. Although it was only available in 100 metropolitan areas worldwide, it became a hit among early adopters. The growth accelerated after Foursquare allowed users to check-in from anywhere in the world in January 2010, with new features being added regularly. Foursquare hit 5 million members at the beginning of December, and it was confirmed at the end of January that it had 6 million users. With the 7-million mark in clear sight, it appears that Foursquare’s growth is rapidly speeding up, to resemble a hockey stick-type curve.

[Image Credit flickr, seanaes]