Ilonen, who last won at the same event in 2007, carded a three-under par 69 to finish with a 21-under total at the Bro Hoff Slott Golf Club.
Jonas Blixt was the best of the Swedish contingent in second after a 72 on the final day left him 18-under.
Austria's Bernd Wiesberger finished third, a shot further back, while Denmark's Thomas Bjorn ended in a four-way tie for fourth at 16-under with Swedes Alexander Noren and Rikard Karlberg and Italian Matteo Manassero.
Ilonen's victory was set up on Friday with a stunning second round nine-under par 63. He followed it up with a 65 to put him in the driving seat.
A bogey on the 12th hole was Ilonen's only blemish on the final day but birdies either side of the blip before five straight pars ensured there would be no last day meltdown.
In contrast to Ilonen's consistent performance, Blixt entertained the crowds with a topsy-turvy back nine. He made four birdies but gave all the shots back with two bogeys and a double bogey to prevent him making a run at the title.
Another Swede, Noren, looked the player most likely to haul in Ilonen and his chances were bolstered as he birdied the same 12th hole where the Finn had struggled.
But when Noren found the water on the 15th to register a double-bogey seven his challenge faded away, leaving Ilonen to take home the trophy.
Final leaderboard (top 10):
1. 267 Mikko Ilonen (Finland) 70 63 65 69
2. 270 Jonas Blixt (Sweden) 70 66 66 68
3. 271 Bernd Wiesberger (Austria) 69 72 64 66
4. 272 Thomas Bjorn (Denmark) 70 67 68 67
-- 272 Rikard Karlberg (Sweden) 69 68 67 68
-- 272 Matteo Manassero (Italy) 66 65 71 70
-- 272 Alexander Noren (Sweden) 67 69 64 72
8. 273 Ross Fisher (Britain) 72 67 70 64
9. 274 Felipe Aguilar (Chile) 71 67 70 66
-- Julien Quesne (France) 73 67 66 68