Rental prices increased by 2.7% nationally to stand at an average of €1,256 a month by the end of last year, according to the latest figures from the Residential Tenancies Board.
That compares to an increase of 6.4% in 2019.
Dublin had the highest rents where the average price was €1,745 per month, a 2.1% increase year-on-year.
But the RTB said that rent prices fell by 0.8% between the third and fourth quarters of the year.
The counties with the lowest monthly rents were Donegal and Leitrim at €626 a month.
During the fourth quarter of 2020, eight counties had standardised average rents above €1,000 a month - Cork, Dublin, Galway, Kildare, Limerick, Louth, Meath, and Wicklow.
The fastest growing rent in the fourth quarter of 2020, by county, was seen in Co Longford (8.3%) and the county with the largest year-on-year decline in rents was Waterford, with rents there down 13%.
Today's figures show that new tenancies continued to account for about four-fifths of all registrations at 82.8%, with 17.2% of registrations representing tenancy renewals.
Padraig McGoldrick, interim director of the RTB, said the impact of Covid-19 on the rental sector continued into the fourth quarter of 2020.
He added that the national standardised average rent remained static in the quarter and, overall, in the year there had been a significant trend of moderation in rental inflation relative to previous years.
Mr McGoldrick said that while there has been a definite trend in moderation in rent levels, it is clear affordability issues and related risks remain.
"We understand that Covid-19 presents many challenges and adjustments for those operating and living in the rental sector," he said.
"We continue to encourage those who are experiencing issues in their tenancies to keep lines of communication open and if they still cannot resolve their dispute to contact the RTB for support and information on how to resolve these matters," he added.
Padraig McGoldrick also highlighted that further measures and the extension of temporary protections for those impacted by the pandemic were introduced by Government towards the end of last year.