Alicante, Hamburg and Berlin were the destinations which saw the biggest rise in passenger numbers compared with the same month last year.
Stansted, which also part of the Manchester Airports Group, achieved a 7% increase to 2.3 million passengers on the back of Jet2.com southern base experiencing a strong second month.
Ryanair and easyJet also grew passenger numbers at the Essex terminal.
The most popular countries to fly to from Stansted were Spain, Italy, Germany and Poland.
East Midlands and Bournemouth airports also grew passenger numbers during the month, with East Midlands up by 3.9% to 503,000 and Bournemouth growing 4.7% to 74,112.
Andrew Cowan, Stansted chief executive, said: “The strong growth in passenger traffic at the start of the summer season continued in May as we welcomed nearly 2.3 million to Stansted, up 7% on 2016 and more passengers for the month than in any previous year.
“As we head into the main summer period we expect this trend to be maintained with the number of flights already scheduled by our airline partners across the peak months up by around 10% over last summer.
“With passengers clearly wanting to fly from their local airport and take advantage of the 180 destinations on offer, we continue to plan how we meet future passenger growth, add vital capacity and invest in our facilities to provide the best customer experience.”