| Oak Ridges Trail Association, Caledon Chapter | King City |
| Oakville Physiotherapy Centre | Oakville |
| Oakwood Academy | Meadowvale |
| Oasis Centre des Femmes | Brampton |
| Office of the Independent Police Review Director | Toronto |
| Office of the Ombudsman of Ontario | |
| Olive Grove School | Erin Mills |
| Oliver House | Caledon |
| Ontario Addiction Treatment Centres, Brampton Clinic | Brampton |
| Ontario Autism Program (OAP) | Ontario |
| Ontario Aviation Historical Society, Great War Flying Museum | Cheltenham |
| Ontario Camps Association | Toronto North |
| Ontario College Application Services | Guelph |
| Ontario Diagnostic Centre (ODC) - Etobicoke - Humber College Blvd | Etobicoke North |
| Ontario Diagnostic Centre (OCD) - Brampton | Brampton |
| Ontario Diagnostic Centre (ODC), Etobicoke - Rexdale Blvd | Etobicoke North |
| Ontario Diagnostic Centre (ODC) - Etobicoke - Albion Rd | Etobicoke North |
| Ontario Diagnostic Centres, Mississauga - King St | Mississauga |
| Ontario Diagnostic Centres, Radiology Associates, Square One | Mississauga |
| Ontario Diagnostic Centres - Clarkson | Mississauga |
| Ontario Federation of Anglers and Hunters | Peterborough |
| Ontario Federation of Teaching Parents | Gananoque |
| Ontario Genealogical Society, Halton Peel Branch | Mississauga |
| Ontario Home Health, Ontario Home Oxygen and Respiratory Services | Orangeville |
| Ontario Learning Development Foundation Inc., Peel Summer Camps | Peel Region |
| Ontario Lottery and Gaming Coorporation, OLG | Toronto |
| Ontario March of Dimes, West Central Regional Office | Mississauga |
| Ontario Medical Imaging, Georgetown | Georgetown |
| Ontario Ministry of Community Safety and Correctional Services, Ontario Correctional Institute | Brampton |
| Ontario Ministry of the Solicitor General, Office of the Chief Coroner, Regional Supervising Coroner's Office, Central West Region | Guelph |
| Ontario Ministry of Transportation, Driver Examination Centres, Etobicoke Centre | Etobicoke Central |
| Ontario Ministry of Transportation, Ontario Drive Test Centre-Orangeville | Orangeville |
| Ontario Pet Loss Support Group | Mississauga |
| Ontario Provincial Police, Caledon Criminal Investigative Services | Caledon Village |
| Ontario Provincial Police, Caledon Detachment | Caledon East |
| Ontario Registered Music Teachers' Association | Bolton |
| Ontario Tenants Rights, Housing Information | Peel Region |
| Ontario Track 3 Adaptive Sports Association | Toronto |
| Ontario Travel Clinic | |
| Ontario Universities Application Centre | Guelph |
| Ontario Volunteer Centre Network | Ontario |
| Ontario. Employment Ontario, Apprenticeship Office, Central Region, Mississauga Apprenticeship Office | Mississauga |
| Ontario. Ministry of Advanced Education and Skills Development, Employment Ontario Contact Centre | Toronto |
| Ontario. Ministry of Children, Community and Social Services, Adoption Disclosure Registry | Toronto Central |
| Ontario. Ministry of Children, Community and Social Services, Adoption Unit | Toronto Central |
| Ontario. Ministry of Children, Community and Social Services, Central Region, Special Services at Home (SSAH) | Mississauga |
| Ontario. Ministry of Children, Community and Social Services, Central West Region | Mississauga |
| Ontario. Ministry of Children, Community and Social Services, Family Responsibility Office | Mississauga |
| Ontario. Ministry of Children, Community and Social Services, Ontario Disability Support Program, Employment Supports, Brampton Office | Brampton |
| Ontario. Ministry of Children, Community and Social Services, Ontario Disability Support Program, Income and Employment Supports, Mississauga Office | Mississauga |
| Ontario. Ministry of Children, Community and Social Services, Ontario Works | Peel Region |
| Ontario. Ministry of Children, Community and Social Services, Youth Justice Services, Brampton Youth Probation Office | Brampton |
| Ontario. Ministry of Children, Community and Social Services, Youth Justice Services, Mississauga Office | Mississauga |
| Ontario. Ministry of Community Safety and Correctional Services, Probation and Parole Services, Brampton Office | Brampton |
| Ontario. Ministry of Government and Consumer Services, ServiceOntario, INFOline | Toronto Central |
| Ontario. Ministry of Government Services, Archives Of Ontario | Toronto |
| Ontario. Ministry of Government Services, ServiceOntario, Provincial Office | Thunder Bay |
| Ontario. Ministry of Labour, Employment Standards | Mississauga |
| Ontario. Ministry of Labour, Occupational Health and Safety, Central Regional Office, Peel District Office | Mississauga |
| Ontario. Ministry of Natural Resources, Niagara Escarpment Commission, Georgetown Office | Georgetown |
| Ontario. Ministry of the Attorney General, Central West Region, Peel Region, A Grenville & William Davis Courthouse | Brampton |
| Ontario. Ministry of the Attorney General, Family Justice Matters, Office of the Public Guardian and Trustee | Toronto Central |
| Ontario. Ministry of the Attorney General, Office Of The Children's Lawyer | Toronto Central |
| Ontario. Ministry of the Attorney General, Ontario Court Of Justice, Provincial Division, Family Court | Brampton |
| Ontario. Ministry of the Attorney General, Victim Support Line | Toronto |
| Ontario. Ministry of the Environment and Climate Change, Spills Action Centre | North York Central |
| Ontario. Ministry of Training, Colleges and Universities, Ontario Student Assistance Program | Thunder Bay |
| Ontario. Ministry of Transportation, Accessible Parking Permit | Ontario |
| Ontario. Ministry of Transportation, Driver Examination Centres, Brampton Centre | Brampton |
| Ontario. Ministry of Transportation, Travel Information (511) | Ontario |
| Open Arms Preschool & Early Learning Centre | |
| Open Book Childcare Centres Inc. | |
| Open Book Daycare Centres Inc. | Brampton |
| Opportunities Mississauga for 21 Plus | Mississauga |
| Optimist Club, Optimist Club of Caledon | Caledon Village |
| Options Mississauga | Mississauga |
| Orange Care Pharmacy, Orangeville - Lakeview Crt | Orangeville |
| Orangeville and District Horticultural Society | Orangeville |
| Orangeville and District Seniors Centre | Orangeville |
| Orangeville Christian School | Orangeville |
| Orangeville Family Footcare | Orangeville |
| Orangeville Family Medical Centre | Orangeville |
| Orangeville Food Bank | Orangeville |
| Orangeville Foot Clinic | Orangeville |
| Orangeville Hearing Clinic | Orangeville |
| Orangeville Medical Imaging | Orangeville |
| Orangeville Medical Imaging, Ontario Breast Screening Program (OBSP) | Orangeville |
| Orangeville Public Library, Alder St Branch | Orangeville |
| Orangeville Public Library, Main Branch | Orangeville |
| Orangeville Speech and Language Clinic, Kindrey Rowland and Associates | Orangeville |
| Osteoporosis Canada | Canada |
| Our Lady of the Airways Church | Malton |
| Our Place Peel, Emergency Youth Shelter, Transitional Program | Mississauga |
| Overeaters Anonymous | Peel Region |
| Oxford Learning Centre - Meadowvale | Meadowvale |
| Oxford Learning Centre - Springdale | Bramalea |
| Oxford Learning Centre Bolton | Bolton |