Just over 13,500 people were in emergency accommodation last month in new record figures.
A total of 13,531 people - including 6,308 single men and women - were accessing local authority managed emergency accommodation in January.
The figure also includes 4,027 children.
December figures showed there were 13,318 people in emergency accommodation at Christmas.
There are now 1,940 families in emergency accommodation, 24 more than in December 2023.
Meanwhile, the number of homeless families is up 21% on January 2023.
A homeless person begging on a street in Dun Laoghaire, Co Dublin in January 2021. Picture by: NurPhoto SRL / Alamy Stock PhotoFocus Ireland CEO Pat Dennigan said the figures are a 'serious setback' after the welcome fall in family homelessness before Christmas.
"Not only are there 4,027 children homeless but more of them were also homeless for longer, increasing the harm that homelessness can cause," he said.
"Homelessness causes great suffering for all those affected, with children bearing the brunt of its harm.
"It is truly heartbreaking that 4,027 children were homeless in January, an appalling situation which, without the right support, can have a lifelong impact.
"As a society, we must move beyond mere expressions of disappointment at the persistently record-breaking homelessness figures each month," he added.
Mr Dennigan said it is time to take "meaningful actions" that will cause change - such as ensuring a fairer allocation of social housing for families who are homeless.
'Single people in particular'
Depaul Chief Executive David Carroll also said now is the time to make changes.
"It will become clearer in the coming months but underlying trends suggest that we may be able to achieve some inroads in reducing aspects of homelessness this year, particularly family homelessness," he said.
"The high level of those emerging from the single adult cohort continues to concern us and structural responses are needed to address the needs of this vulnerable cohort."
Mr Carroll said single people are being left with fewer options.
"Whilst we greatly welcome news of a positive uplift in new home starts, there continues to be a lack of housing options for single people in particular," he said.
"Many single adults are being forced to sleep rough if homeless accommodation is not available and they have no family or friends to turn to.
"The need for increased social housing stock is evident and must be prioritised for those most in need - targeted development for the single cohort is critical," he added.
Mr Carroll said the charity is "looking forward" to the publication of the Housing Commission's final report.
