The Irish star bought a key piece of retail estate in Palm Beach Gardens, which counts golf pros Tiger Woods and Jack Nicklaus as residents and investors.
Rory (23) had been looking for a home in the region for many years and is said to be keen to establish a love nest with girlfriend and tennis pro Caroline Wozniacki.
The move is significant for the athlete, who put his Northern Ireland bachelor pad in Holywood, Co Down on the market for more than €1.8m.
The 10,000 sq ft Florida house is described by real estate agents as a family home, with a playroom designed for children.
The home was on the market for €8.4m and it is believed that Rory paid close to the asking price.
The six-bedroom, nine-bathroom house is on two levels and includes a guest house for visiting friends and family.
The house is surrounded by a putting green and palm trees for privacy.
The home, described as "gated, private and elegant", has its own private jetty in deep water.
McIlroy has been renting in the area for many years.
The golfer has thought about selling his home in Co Down for a while. The decision was made "for practical and commercial reasons".
Situated at Moneyreagh in the hills above Belfast, the five-bedroom property includes a practice area with a putting green and driving range.
There is also a gymnasium in an adjoining refurbished stone barn. The house -- set in 14 acres -- was built in 2006.
McIlroy bought the house in 2009, but now spends most of his time overseas, playing the bulk of his golf in the United States.
The top-ranked player in the world made €10.8m in earnings this year on the PGA Tour and European Tour.