The Simon Community provided support to more than 16,000 people in 2018 - and the organisation fears the number will only increase.
Last year saw a 24pc increase in the number of people using the homeless charity's services, a figure the Simon Community has described as "shocking" and the highest number for a single year.
However, the organisation now fears the number for 2019 will be higher again with a record number of people homeless in Ireland.
Its annual report showed 16,776 people used the Simon Community's services in 2018. The figure included 2,834 families with 5,331 children and compared with 13,304 the previous year.
The report was released as thousands took to the streets of Dublin and Cork yesterday to protest at homelessness.
One protester, who rents a house under the Housing Assistance Payment (HAP) scheme, said she fears that her landlord could decide to sell her house, leaving her and her family homeless.
"I'm in a landlord's accommodation and I'm terrified that he's going to come along and say, 'I'm selling the house'," she said.
"The place is freezing, he's allowed to get away with murder and he's getting so much rent.
"I'm with HAP now. I pay just a little under €100 into his bank account every week, so he's getting €1,300 off HAP and then I pay €100 a week."
National spokesman for the Simon Community Wayne Stanley said the figures were shocking but a recent drop in homelessness was welcome.
He added the homeless figures were being driven by increased family homelessness in Dublin.
"Last year saw 16,776 people provided with support by Simon," he said.
"That is more individuals and families than ever before, a startling 24pc increase on 2017.
"Worryingly, all the indications are that 2019 numbers will exceed 2018.
"These increases are shocking, but we are also proud that many of these individuals and families have been prevented from having to enter homeless services with the support of Simon."
He added recent figures showed a drop in homelessness of about 23 families in Dublin in October which reflected better co-ordination among providers, rather then less demand.