Eighteen pub closures, an average of more than one per month, put Mayo at the top of the national ladder for under-age drink prosecutions.
Licensees convicted by the District Court were fined thousands of pounds in total and barred from trading for a cumulative 75 days.
Chief Supt John Carey said: "Garda∅ have gone undercover in special operations to detect offenders and will continue doing so, particularly in the run-up to Christmas".
One publican, however, has since appealed a £1,000 fine and a 14-day closure order. This appeal will be heard in the Circuit Court in the new year.
Since tougher new legislation was enacted last year, four publicans in Westport have been closed down by a District Court judge for periods ranging from two to three days.
Three pubs in Louisburgh were shut for periods ranging from two to five days.
The closure of three pubs in Ballina was ordered by the District Court, one of them for a period of seven days.
A prominent Castlebar venue was closed for five days in March.
The following month, a £1,000 fine and a 14-day closure order was imposed on the same premises. These have been appealed to the Circuit Court.
A central Mayo publican who runs a disco was fined £1,200 last month and his premises was closed for seven days.
Other licensees against whom successful prosecutions were taken and closure orders implemented were in Belmullet, Crossmolina, Foxford, Knock and Kiltimagh.