The Finn followed up stunning performances on days two and three at the Bro Hof Slott Golf Course to walk off with the title by three shots from Jonas Blixt.
Ilonen had carded rounds of 70, 63 and 65 heading into the final day and continued to make his mark, sinking birdies on the second, third, 11th and 13th holes to go round in three-under 69.
His only blemish came with a bogey six on the 12th but that did little to dent his overall tournament score of 21 under.
Ilonen's last success came at the Scandinavian Masters in 2007 and he admitted a good night's sleep contributed to Sunday's success.
"I slept brilliant. I was pretty tired after yesterday, yesterday was the toughest day of them all I think," he said.
"I have my family here with me. My boy's gone to sleep about 8.30pm and I went off about 9pm, so I slept pretty good all the way through to about 6.30am.
"It's pretty special. I could feel a lot of support from Finland, especially today.
"Playing with Alex (Sweden's Alexander Noren) in the last group in front of the local fans, it feels pretty special."
Not even a lapse in concentration on the 12th green, where he fluffed a short putt, could knock the 33-year-old out of his stride.
He said: "I just got ahead of myself a little bit with the first putt.
"I've said it for weeks now, it doesn't really bother me if make a bogey, a birdie or par. As long as I have holes to play I know I can make it up and I did."
Blixt tried his hardest to catch Ilonen, carding an eagle on the par-five ninth, but dropped shots on the 11th and 14th plus a double bogey on the 13th saw him come up short with a four-under 68.
A six-under 66 from Bernd Wiesberger ensured the Austrian rounded off the top three, a further shot adrift, while Thomas Bjorn was among the Nordic contingent to grace the leaderboard following his round of 67.
The Dane carded six birdies to one bogey to finish in a four-way tie for fourth on 16 under, alongside Swedes Rikard Karlberg and Noren plus Italian Matteo Manassero, who was looking to add to his success at last weekend's BMW PGA Championship.
England's Ross Fisher also made tremendous strides on the final day to finish on the leaderboard, albeit six shots off the pace.
The 32 year old sank eight birdies in a flawless round for a score of 64 and 15 under overall.