An ever increasing number of desperate families complained their loved ones are at risk of ending up in a homeless shelter or jail because there is nowhere to care for them, said Marin.
"We have heard heart-wrench stories from aging or ill parents whose adult sons and daughters are a danger to themselves and others and need constant care that can't be provided at home, but they have nowhere to turn," he said in a statement.
"Many complained of a lack of planning and funding, lengthy delays and poor co-ordination of care through agencies contracted by the Ministry of Community and Social Services."
A Sarnia woman whose husband is dying from cancer held a news conference last month to say her family was told to put their disabled adult daughter into a nursing home or give up custody if they want her to remain in a group home.
Wilma Arthurs, 58, said it was devastating to realize she and her husband Chris, who has colon cancer, could no longer care for Emilia, 21, who suffered brain damage as an infant that left her with epilepsy, deafness and severe autism.
"Some of these caregivers are on the brink of emotional and physical breakdown," said Marin.
"We have investigated past cases where people with these severe disabilities have been sent to shelters and even jail."
Many parents of adult children with severe special needs complained that services for them essentially vanished when the kids turned 18.
Some families complained they were refused support services because of their child's high needs and challenging behaviours, and some aging or ill parents are at risk themselves and have nowhere to turn, added Marin.
The ombudsman said complaints about the Ministry of Community and Social Services' response in such situations have steadily increased, from 35 in 2010 to 64 so far this year.
"What is particularly troubling is that the complaints have only gone up, despite new legislation and changes made by the ministry in recent years," said Marin.
"The increase in complaints indicates there may be a systemic problem and a broader investigation is warranted."
Social Services Minister John Milloy was not available for comment Thursday, but issued a statement defending the government's services to developmentally disabled individuals.
"My ministry works tirelessly with all individuals, their families, community agencies and across government to find appropriate placement or services with the appropriate level of care, including for those whose needs are most acute," said Milloy.
"I can assure you that we don't give up looking for solutions and work together to ensure that a client is never left at risk."
Services for adults with developmental disabilities in Ontario are provided by 300 community-based agencies contracted and funded by the ministry.
The ombudsman's investigation, which will take about six months, will look into whether or not the ministry is adequately responding to urgent situations and whether it's doing enough to co-ordinate and help families access services.