Tight security marked the wedding of the 27 year old Down born golfer and his 29 year old fiancée as both insisted they wanted the evening celebration to be strictly private.
More than 200 guests are attending the sumptuous wedding at the 350 acre estate.
Amongst the celebrities in attendance are Ryder Cup golfers Sergio Garcia, Paul McGinley, Martin Kaymer and Shane Lowry.
Mr McIlroy's good friend, One Direction star Niall Horan, was also in attendance.
It is reported that actor and 'Forty Shades of Grey' star Jamie Dornan will also attend.
Pop star Ed Sheeran is tipped to attend the post-wedding celebrations tomorrow due to concert commitments today.
The world of business was represented by Limerick billionaire JP McManus.
Music will be provided later tonight by US pop and soul legend, Stevie Wonder (66), who was specially flown in to Mayo for the event.
The star will be supported by a full orchestra for his performance.
The lavish gourmet wedding menu is being supervised by Ashford Castle executive chef Philippe Farineau.
Over the past 48 hours, a fleet of limousines, jeeps and helicopters swept into Cong in preparation for Ireland's celebrity wedding of the decade.
Dozens of locals gathered outside the main entrance gate to Ashford Castle today hoping to catch a glimpse of the celebrities.
Erica was even offered best wishes and a little advice as Limerick-born teacher, Aoife Power, posed for photos outside the Ashford Castle gates with her hen party.
Aoife, who teaches in Lucan in Dublin, will marry Ian Barron on June 16.
"I just want to wish Rory and Erica the very best," the Castletroy native said.
One of her hen party friends also offered a little marital advice to the New York-born bride.
"Keep the dinner cooked and the kitchen clean," she laughed.
At one point, more than a dozen cheering One Direction fans also gathered hoping to meet Niall Horan.
The wedding will also feature a major fireworks display later this evening.
Locals admitted they were thrilled with the focus on the picturesque village.
"It is great for Cong, great for Mayo and great for the West of Ireland," admitted Aisling Butler who runs 'The Hungry Monk' cafe with Jonathan Byrne.
"Everyone is keeping their eyes peeled for a celebrity - and, to mark the occasion, I was was even thinking of selling golf balls in the cafe with morning coffee."
Aisling's cafe is already a popular haunt with Irish celebrities with regular visitors including Daniel O'Donnell, The Hardy Bucks, Pipp O'Connor and Connacht rugby stars.
Local man Paddy Rock, who founded the Cong Hands of Fame Award, said the golfer's contribution to the area is such that he is now being invited to immortalise himself by having his hand imprint set in bronze on the monument.
Locals raced for their cameras as a vintage but empty wedding car - with the fitting license plate '2R1' - drove through the town towards Ashford Castle.
Mr McIlroy's management team have worked overtime to ensure the wedding details remained top secret from the large media entourage which has descended on Cong.
The castle went into full security lock-down yesterday morning as the last of the non-wedding guests left.
Special security wristbands were issued to allow access to the 350 acre estate until Monday morning when the wedding party formally ends.
Three separate layers of security were in place around the estate including perimeter patrols.
Mr McIlroy's personal security chief, Brian Murphy, who also works with U2, was supervising arrangements at the castle perimeter.
Staff at Ashford Castle have been issued with green wristbands - while other colours will designate wedding organising staff, security and entertainers.
A large marquee was erected outside the castle though the majority of the wedding ceremonies will happen inside the huge luxury hotel.
The lavish four day wedding celebration is understood to cost between €250,000 and €500,000 - with Ashford Castle and virtually all hotels and guest houses in nearby Cong block booked for the wedding.
Wedding guests arriving early at the main Ashford Castle entrance were greeted by a staff member in formal attire including butler's hat.
The majority of guests flew into Shannon and Knock Airports and were transferred by limousine to Cong.
A small army of caterers and wedding planners - most of whom are staying at Ryan's Hotel in Cong village - were hard at work for Saturday's ceremony.
Even teams of street cleaners were working to have all approach routes to Ashford Castle spotless.
The wedding party travelled to Cong village on Wednesday.