Prices nationally were down by 0.5pc annually in July, according to the Central Statistics Office.
It was the first annualised fall since May 2013, economists said.
In the month of July prices were up slightly, by 0.3pc, the statisticians revealed.
However, there was a sharp fall in the number of transactions in the month.
Prices had holding been holding steady up to now despite the chaos caused to the economy by the pandemic.
Prices had risen in April and May but had been flat in June.
Experts said the impact of the coronavirus on the market had taken a while to kick in as the price index is based on stamp duty filings, and solicitors can take a while to send them to Revenue.
In Dublin, residential property prices saw a decline of 1.3pc in the year to July, according to
When Dublin is excluded prices were 0.2pc higher in the year to July, with house and apartment prices both up.
The region outside of Dublin that saw the largest rise in house prices was the South-West at 4.3pc. At the other end of the scale, the South-East saw a 1.6pc decline.
In July, 2,561 household dwelling purchases were filed with Revenue. This represents a 41pc decrease compared with July last year.
The total value of transactions filed in July was €767m.
Households paid a median price of €259,000 for a home in the 12 months to July 2020.
The Dublin region had the highest median price at €375,000.
Within the Dublin region, Dún Laoghaire-Rathdown had the highest median price at €530,000, while South Dublin had the lowest at €347,500.
The highest median prices outside of Dublin were in Wicklow at €335,000 and Kildare at €305,011, while the lowest price was €108,000 in Leitrim.