The couple’s big day is being billed as the wedding of the year, with a lavish ceremony planned for today behind the walls of the 13th century Ashford Castle.
McIlroy, from Holywood, Co Down, revealed in a recent interview that he was friends with Ms Stoll before romance blossomed.
She got the star to the first tee on time for his singles match in the 2012 Ryder Cup Miracle in Medinah after he overslept.
Ms Stoll, from Naples, Florida, who is the manager of championship volunteer operations at the PGA of America, came to his rescue before police rushed him to his course.
It is no surprise that the couple, who started dating in 2014, chose Ashford Castle for their wedding.
The pair stayed in the luxury hotel in Cong, Co Mayo, on New Year’s Eve in 2014 and have returned every year since.
However, McIlroy chose to pop the question during a romantic dinner in Paris two years ago.
The hotel and 350-acre estate were booked from Wednesday for the four-day wedding party expected to cost more than €500,000.
Coldplay, Ed Sheeran and U2 are some of the acts rumoured to play at the weekend.
Stevie Wonder could also make an appearance — Ms Stoll is a huge fan of the soul and pop star.
Hairdresser Ann-Marie Harie, who owns Harie’s Kutz salon in Cong, said local people enjoyed the buzz but were always well-mannered.
“It’s nice to see the celebrities around, but we don’t bother them and that’s probably the reason they keep coming back,” said Ms Harie.
The couple always wanted to keep their big day private and security has been tight at the hotel all week.
A special marquee has been erected in the castle ground to accommodate wedding guests. However, the wedding ceremony itself is expected to take place inside the hotel.
Best man will be McIlroy’s childhood pal, Harry Diamond, who organised the stag party in Miami last weekend.
Ms Stoll’s family and friends are believed to have flown into Shannon over the last couple of days.
The golfer and Ms Stoll will have the presidential suite once occupied by US president Ronald Regan when he stayed at the hotel during his 1985 Irish visit.
Locals are hoping that McIlroy will take a break from his wedding celebration to leave a permanent mark on the village.
Organiser of the Cong Hands of Fame Award, Paddy Rock, said space had been set aside for the four-time major winner to immortalise his handprints in bronze on a wall.
“If he didn’t want to do it, we wouldn’t think any less of him,” Mr Rock said.