Over 60% of flights from Shannon, Kerry and Knock are to the UK
Irish air traffic grew by 7.5% - or 81,373 movements - in January 2017, compared to the same month last year.
The Irish Aviation Authority (IAA) say this continues the strong performance of 2016.
Within that figure, there was an increase of 5.3% in Ireland's overflight traffic movements - these are flights which do not land in Ireland - while Europe/US flights recorded an increase of 8.5% in January.
There were 24,682 overflight traffic movements and 35,661 Europe/US flights during the month.
Eamonn Brennan, chief executive of the IAA, said: "We are delighted to see air traffic in 2017 getting off to a strong start, building on the very encouraging gains of last year.
"Up to 90% of transatlantic air traffic passes through Irish-controlled airspace, so I am particularly pleased with the strong growth in our en route traffic.
"On the domestic front, terminal air traffic at Dublin and Shannon continues to increase strongly with growth of 4.3% and 5.6% recorded respectively in January."
In terms of domestic air traffic, the combined figure for commercial flights at Shannon, Dublin and Cork airports was up by 3.8% in January 2017.
Individually, the January 2017 figures for the three State airports - when compared to the same month in the previous year - are:
However, Mr Brennan also said this performance could be hampered in the years ahead as a result of Brexit.
He added: "Air connectivity between Ireland and the UK is hugely important to the Irish economy both for tourism and trade.
"The UK market accounts for over 60% of the capacity from Shannon, Kerry and Knock and for over 40% of all the passengers from Dublin.
"Indeed, if we look at the number of business trips we have via air travel across the whole of the EU, 44% are with the UK."
Air connectivity all over the world is based on Air Service Agreements and once the UK leaves the EU a new Air Service Agreement will have to be put in place between the EU member states and the UK.
The IAA say if that agreement constraints the ability to fly easily between Ireland and the UK, or for Irish airlines to operate freely around the EU, then that will be bad for the Irish economy.
"It looks like we are heading for a hard Brexit so it's really vital that aviation is at the forefront of the negotiations from an Irish perspective", Mr Brennan continued.
"That's very important as the rest of the EU might not share the same view as us.
"Brexit does offer some opportunities to Ireland, such as increasing the attractiveness to transit through Ireland to North America rather than the UK and our airports will be seeking to capitalise on that but in broader terms a hard Brexit will be difficult for the Irish civil aviation industry."