There were 12,691 people registered as homeless in the State last month, new figures show.
Some 1,886 of these were families and 3,895 were children.
This is an increase of 152 people in emergency accommodation since July.
Simon Communities Executive Director Wayne Stanley is calling for significant investment in the upcoming budget.
"The focus now must be on Budget 2024 that will be announced on the 10th of October," he said.
"That is the next landmark moment that will tell us how the Government plans to prioritise housing and homelessness.
"If the State is to meet its commitment to address homelessness by 2030, now is the time to make a real difference to the lives of those experiencing or facing homelessness.
"The budget must deliver a significant investment in homelessness prevention, increases funding to ensure that support services are maintained and enhanced and that the State quickly moves to ensure delivery of a minimum of 15,000 social homes each year," he added.
Depaul Chief Executive David Carroll said the figures highlight the severity of the crisis.
"Depaul wants to see Temporary Accommodation being used as little as possible but worry the situation will become progressively worse unless adequate funding, and resourcing is allocated in Budget 2024," he said.
"Homelessness is solvable and Budget 2024 is critically important for those in temporary accommodation or on the cusp of homelessness.
"We are seeing thousands of households stuck in the temporary accommodation system, sadly in some cases, for years.
"People are suffering from this lack of movement and this must be prioritised this October," he added.