The State's planning board decided 25% of cases within statutory timelines last year compared to 28% a year earlier, according to its annual report.
In most cases the statutory objective period is 18 weeks, however, in some cases it is four months.
It said the reduction in the number of cases handled in the statutory period reflected how the organisation concentrated on clearing the older cases.
An Coimisiún Pleanála said so far this year 50% of cases were being dealt with within statutory timelines.
The total average number of weeks that it took to decide all planning cases in 2024 was 41.7 weeks.
An Coimisiún Pleanála said it had reduced the number of open planning cases by 38% last year.
It said the number of planning cases dealt with last year also increased by 12.8%.
The organisation is under new management after it was hit by significant governance issues over recent years.
Its chief executive Peter Mullan said that it introduced reforms following a review by the Office of the Planning Regulator.
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It has also increased staff numbers by 40 to 290.
It said all Large Scale Residential Development cases were dealt with within the statutory 16 weeks meaning there was no delay in relation to applications under this scheme.
The organisation's chairman, former HSE boss Paul Reid, said: "With new and enhanced governance structures embedded in the organisation our focus is to continue building on the strong performance recorded in 2024".
"We are determined to reach the targets and timelines set for decision-making under our new legislation," he added.
He added the organisation is rolling out a new digital appeals service.
