The user statistics for the year ending the end of April - which also marked its three year anniversary - are said to signal the first time the average for a whole year has reached over a million a month.
The latest figures available, which relate to all content tagged as data, also show around 1.6 million page impressions a month on average for the past year.
Editor of the Datastore and Datablog Simon Rogers told Journalism.co.uk: "For us, what started off as an exercise for developers has proved really successful with the general readership too, who just really like what we do I guess."
"We're quite open about what we do, we use free tools and we make it available for everybody and we try and do something that can be replicated, so anybody can do what we do and that's kind of been a crucial part of it.
"People do say 'is there a model for making data journalism work economically?' ... We've shown it can be viable in those commercial terms as well."
Earlier this month Rogers spoke to us about open data and journalism, and offered advice for journalists interested in working with data more.
At the time he said the range of tools available online means money and time do not have to be an issue.
"We're probably the cheapest editorial department at the Guardian. We don't get that much development time. Actually we don't cost a lot of money but use a lot of free tools.
"There's no excuse not to use Google Fusion Tables or things like Tableau Public, these things are free. You can make a map in 20 minutes and we're noticing people picking up these things and using free tools on sites dead quick."
And he added that the inclusion of visualisations to a story also makes it more likely readers will spend time looking at an article.
"Most times visualisation of some kind is worth it, even if it's little, a bar chart can do wonders for you. It doesn't have to be an overcomplicated, massive, great interactive, it can just be a pie chart or a bar chart and that's often enough."
Journalism.co.uk runs training in data journalism. Paul Bradshaw will be leading two one-day courses in September. There are details on the two data journalism days and courses and other short courses at this link.