A Turkish Airlines flight from Houston, Texas, diverted to Shannon was found to have no explosive devices on board and would take off to Istanbul soon, a spokesman for the flag carrier said.
The plane, bound for Turkey's largest city, was diverted after a piece of paper with "bomb" written on it was discovered in the toilet, a spokesman for Turkish Airlines said.
The jet landed at 11.02am in Shannon where it was met by emergency services.
The Boeing 777 was directed to a remote parking location where passengers disembarked and were carried by bus to the airport terminal.
Nothing was found in the search of the aircraft in Shannon, the Turkish Airlines spokesman said, adding that the plane would take off again to Istanbul.
An airport spokesman said the Boeing 777 touched down without incident and all 209 passengers, plus crew, disembarked safely.
"The incident is now the subject of a follow up investigation from An Garda Síochana," the spokesman said.
Turkish Airlines has been targeted with a series of hoax bomb warnings over the last year.