The Kerry and Cork area has the longest waiting list for an appointment with the Child and Adolescent Mental Health Service.
CAMHS is for young people with moderate to severe mental health difficulties.
In November 2021, there were 3,357 people on the waiting list across the country, according to new figures released under the Freedom of Information Act.
Exactly a year later, last November, that had increased by almost 600.
At that point, 218 people were waiting over 18 months, compared to 48 a year earlier.
The Cork and Kerry area is the worst affected. 810 were on the waiting list in November, with nearly a third waiting over a year, and 101 waiting over 18 months.
The Clare, Limerick, North Tipperary and East Limerick area is also badly affected, with the latest data showing 60 people waiting over a year and a half.
Earlier this week, the Mental Health Commission published a damning report into CAMHS, criticising the lack of follow-up care children received.