The number of people in emergency accommodation in August was 10,805, setting another record and up by more than 200 on the July figure of 10,568.
New figures from the Department of Housing show that in the week ending 28 August, there were 7,585 adults and 3,220 children in emergency accommodation.
There were 1,485 families in homeless accommodation, of which 814 - 55% - were single parent families.
Dublin represented 70% of the total, with 5,326 people in emergency accommodation in the county.
Head of Policy and Communication at the Simon Communities of Ireland Wayne Stanley described the figures as "shocking".
The "trajectory of the homelessness crisis heading into the winter months is deeply concerning," he said.
He said the Government needs to take "Covid-19 crisis type actions if we are to reduce the homelessness numbers."
Mr Stanley said the Simon Communities of Ireland are calling for 5,000 vacant properties to be brought into use through the Repair and Lease Scheme for people in homelessness and on the social housing waiting list.
CEO of Dublin Simon Community Sam McGuinness said that the "picture is ominous as we face into the cold, dark winter months ahead and no real clarity or hope in Budget 2023 to support exits out of homelessness."
He said August's figures come at a time when single homelessness is at an all-time high and exits from homelessness are at an all-time low.
Mr McGuinness said that among the people in emergency accommodation in August were older people with complex health needs who never envisaged they would be in that situation and people in employment whose colleagues have no idea they are sleeping in emergency services at night.