| | Organization Name(s) | Located In |
 | Ontario. Members of Provincial Parliament | Toronto |
| | Obtaining a copy of a Certificate of Divorce Decree | Ontario |
 | Ontario. Ministry of Citizenship and Immigration, Ontario Honours and Awards Secretariat | Toronto |
| | Ontario. Ministry of the Environment, Ontario's Drive Clean Program | Pickering |
| | Obtaining a Birth Certificate - Births Outside of Ontario, Overview | Canada |
| | Obtaining a Birth Certificate - Births Outside of Canada, Overview | International |
| | Ontario. Ministry of Health and Long-Term Care, Wait Times in Ontario | Toronto |
| | Oasis Centre des femmes | Toronto |
 | Oasis Egyptian Belly Dance | Stratford |
 | Obstetricians | Stratford |
 | Office of the Ombudsman of Ontario | Toronto |
| | Ogletree, Marlene & David - Cleaning | St Marys |
 | OmbudService for Life and Health Insurance | Toronto |
 | Ombudsman for Banking Services and Investments | Toronto |
 | On Stage Dance Studio | Stratford |
 | Ontario Association of Naturopathic Doctors | Toronto |
 | Ontario Bean Producers' Marketing Board | London |
| | Ontario Block Parent Program, St Marys | St Marys |
| | Ontario Block Parent Program, Stratford | Stratford |
 | Ontario Blue Cross | Etobicoke |
| | Ontario Brain Injury Association | Thorold |
| | Ontario Breast Screening Program - Southwest Region | London |
 | Ontario Camps Association | Toronto |
 | Ontario Canola Growers Association | Guelph |
 | Ontario Civilian Police Commission | Toronto |
 | Ontario Clean Water Agency, Stratford | Stratford |
 | Ontario Coalition for Better Child Care | Toronto |
 | Ontario College of Homeopathic Medicine | Toronto |
 | Ontario College of Pharmacists | Toronto |
 | Ontario College of Teachers | Toronto |
 | Ontario Criminal Injuries Compensation Board | Toronto |
 | Ontario Energy Board | Toronto |
 | Ontario Enhanced Driver's Licence | Toronto |
 | Ontario Federation for Cerebral Palsy, Programs,Services, Donation Pick-up | Toronto |
 | Ontario Federation of Anglers & Hunters. Kincardine | Kincardine |
| | Ontario Genealogical Society, Perth County Branch | Stratford |
 | Ontario Home Health | Stratford |
 | Ontario Human Rights Commission | Toronto |
 | Ontario Interpreting Services, After Hours Emergency Interpreting Service | Toronto |
 | Ontario March of Dimes, Head Office | Toronto |
 | Ontario March of Dimes. London, Home and Vehicle Modification Program | London |
 | Ontario Network for the Prevention of Elder Abuse (The), Elder Abuse Hotline | Toronto |
 | Ontario One Call. Call Before You Dig | Guelph |
 | Ontario Osteoporosis Strategy | Toronto |
| | Ontario Poison Centre | Toronto |
 | Ontario Press Council | Toronto |
 | Ontario Provincial Police, Perth County Detachment | Sebringville |
 | Ontario Psychological Association, Psychologists Referral Service | Toronto |
 | Ontario Retirement Communities Association | Oakville |
| | Ontario Seniors' Secretariat, Seniors' INFOline | Toronto |
 | Ontario SPCA, Perth County Branch | Stratford |
 | Ontario Street Baptist Church, Stratford | Stratford |
| | Ontario Tenants Rights | Toronto |
 | Ontario Women's Directorate | Toronto |
| | Ontario Woodlot Association, Huron Perth Chapter | Huron County |
 | Ontario. Ministry of the Attorney General, Office for Victims of Crime | Toronto |
| | Ontario. Children's Services INFOline | Ontario |
 | Ontario. Consent and Capacity Board, Ontario | Toronto |
 | Ontario. Economic Development & Trade Branch, Entrepreneurship Development, Summer Company Program | Toronto |
 | Ontario. Elections Ontario, Office of The Chief Electoral Officer of Ontario | Toronto |
 | Ontario. Legislative Assembly of Ontario, Office of the Provincial Advocate for Children and Youth | Toronto |
 | Ontario. Legislative Offices, Liberal Party of Ontario, Dalton McGuinty | Toronto |
 | Ontario. Legislative Offices, New Democratic Party of Ontario Leader, Andrea Horwath | Toronto |
 | Ontario. Legislative Offices, Premier Dalton McGuinty, Liberal Party of Ontario Leader | Toronto |
 | Ontario. Legislative Offices. Perth-Wellington, Member of Provincial Parliament, Wilkinson, John | Stratford |
 | Ontario. Ministry of Agriculture Food and Rural Affairs | Guelph |
| | Ontario. Ministry of Agriculture Food and Rural Affairs, Agricultural Information Contact Centre | Guelph |
 | Ontario. Ministry of Agriculture Food and Rural Affairs, Nutrient Management Information Line | Guelph |
 | Ontario. Ministry of Agriculture Food and Rural Affairs, Stratford Resource Centre | Stratford |
 | Ontario. Ministry of Child and Youth Services, Child and Family Services Review Board | Toronto |
 | Ontario. Ministry of Child and Youth Services, Custody Review Board | Toronto |
| | Ontario. Ministry of Children and Youth Services, Bluewater Centre for Youth Justice Services | Goderich |
| | Ontario. Ministry of Children and Youth Services, Ontario Child Benefit | Ontario |
 | Ontario. Ministry of Children and Youth Services, South West Region | London |
 | Ontario. Ministry of Children and Youth Services. Adoption Disclosure, Central Services, Adoption Disclosure Register | Toronto |
 | Ontario. Ministry of Community and Social Services, Assistance for Children with Severe Disabilities | London |
| | Ontario. Ministry of Community and Social Services, Family Responsibility Office | Toronto |
 | Ontario. Ministry of Community and Social Services, Ontario Disability Support Program | Stratford |
 | Ontario. Ministry of Community and Social Services. Social Assistance Programs, Social Benefits Tribunal | Toronto |
 | Ontario. Ministry of Community Safety and Correctional Services, Emergency Management Ontario. Provincial Operations Centre | Toronto |
 | Ontario. Ministry of Community Safety and Correctional Services, Probation and Parole Services, Adults, Stratford | Stratford |
 | Ontario. Ministry of Community Safety and Correctional Services, Stratford Jail | Stratford |
 | Ontario. Ministry of Consumer Services, Consumer Protection Branch | Toronto |
| | Ontario. Ministry of Culture, Ontario Seniors' Secretariat, Senior's Info | Ontario |
 | Ontario. Ministry of Culture, Ontario Trillium Foundation [The] | Toronto |
 | Ontario. Ministry of Education/Ministry of Training, Colleges and Universities, Communications Branch. Public Inquiries Unit | Toronto |
 | Ontario. Ministry of Energy, Home Energy Retrofit Program | Ontario |
 | Ontario. Ministry of Government Services, Access and Inquiry Services | Toronto |
 | Ontario. Ministry of Government Services, Land Registry Office 44 (Perth) | Stratford |
| | Ontario. Ministry of Government Services, ServiceOntario, Specialty Services. Change of Name | Thunder Bay |
 | Ontario. Ministry of Government Services, ServiceOntario, Stratford | Stratford |
 | Ontario. Ministry of Government Services. Central Production and Varification Services Branch | Toronto |
 | Ontario. Ministry of Government Services. Companies and Personal Property Security Branch | Toronto |
 | Ontario. Ministry of Government Services. Office of the Registrar General | Toronto |
 | Ontario. Ministry of Health and Long-Term Care, Assistive Devices Program | Toronto |
| | Ontario. Ministry of Health and Long-Term Care, AIDS and Sexual Health Infoline/The Mainline | Toronto |
| | Ontario. Ministry of Health and Long-Term Care, Health Care Connect | Ontario |
 | Ontario. Ministry of Health and Long-Term Care, Health Information Centre Infoline | Toronto |
| | Ontario. Ministry of Health and Long-Term Care, Ontario Drug Benefit Program | Etobicoke |
 | Ontario. Ministry of Health and Long-Term Care, Ontario Hepatitis C Assistance Plan | Toronto |
 | Ontario. Ministry of Health and Long-Term Care, Trillium Drug Program | North York |
| | Ontario. Ministry of Health and Long-Term Care, www.HealthyOntario.com | Toronto |
| | Ontario. Ministry of Health and Long-Term Care, Your Health Care Options | Ontario |
 | Ontario. Ministry of Labour, Office of the Employer Adviser | Toronto |
 | Ontario. Ministry of Labour. Pay Equity Commission | Toronto |
| | Ontario. Ministry of Municipal Affairs, Landlord and Tenant Board | Toronto |
 | Ontario. Ministry of Municipal Affairs and Housing, Investigation and Enforcement Unit (Maintenance and Standards Section) | Toronto |
 | Ontario. Ministry of Natural Resources, Huron-Perth Area Office | Clinton |
 | Ontario. Ministry of Natural Resources. Angus, Ontario Tree Seed Facility | Angus |
 | Ontario. Ministry of Natural Resources. Peterborough, Outdoors Card Centre | Peterborough (City of) |
 | Ontario. Ministry of Revenue. Client Accounts and Services Branch, Guaranteed Annual Income System | Oshawa |
 | Ontario. Ministry of Revenue. Client Accounts and Services Branch, Ontario Child Care Supplement for Working Families | Oshawa |
 | Ontario. Ministry of Revenue. Client Accounts and Services Branch, Ontario Tax Credit System | Oshawa |
 | Ontario. Ministry of Revenue. Client Accounts and Services Branch, RST Centralized Programs | Oshawa |
 | Ontario. Ministry of Revenue. Hamilton Tax Office, Client Accounts and Services Branch | Hamilton |
 | Ontario. Ministry of Revenue. Kitchener Tax Office, Client Accounts and Services Branch | Kitchener |
 | Ontario. Ministry of Revenue. Whitby Tax Office. Client Accounts and Services Branch | Whitby |
 | Ontario. Ministry of the Attorney General | Toronto |
 | Ontario. Ministry of the Attorney General, Family Law Information Centres, Stratford | Stratford |
 | Ontario. Ministry of the Attorney General, Justice Ontario | Toronto |
 | Ontario. Ministry of the Attorney General, Ontario Court of Justice, Criminal Court Operations | Stratford |
 | Ontario. Ministry of the Attorney General, Ontario Court of Justice, Criminal Court Operations, Listowel | Listowel |
 | Ontario. Ministry of the Attorney General, Ontario Court of Justice, Family Court | Stratford |
 | Ontario. Ministry of the Attorney General, Ontario Court of Justice, Provincial Division | Stratford |
 | Ontario. Ministry of the Attorney General, Ontario Court of Justice, Superior Court of Justice | Stratford |
 | Ontario. Ministry of the Attorney General, Ontario Victim Services Secretariat, Victim/Witness Assistance Program, Stratford | Stratford |
 | Ontario. Ministry of the Attorney General, Superior Court of Justice, Criminal Court Operations, Stratford | Stratford |
 | Ontario. Ministry of the Attorney General, Superior Court of Justice, Family Court, Stratford | Stratford |
 | Ontario. Ministry of the Attorney General, Superior Court of Justice, Small Claims Court, Stratford, Huron St | Stratford |
 | Ontario. Ministry of the Attorney General, Superior Court of Justice, Small Claims Court, Stratford, St Patrick St | Stratford |
 | Ontario. Ministry of the Attorney General. Children's Lawyer | Toronto |
 | Ontario. Ministry of the Attorney General. Office of the Public Guardian and Trustee | Toronto |
 | Ontario. Ministry of the Attorney General. Toronto, Ontario Victim Services Secretariat, Victim Support Line | Toronto |
 | Ontario. Ministry of Tourism | Toronto |
| | Ontario. Ministry of Training, Colleges and Universities, Adjustment Advisory Program | Toronto |
| | Ontario. Ministry of Training, Colleges and Universities, Employment Ontario Hotline | Toronto |
 | Ontario. Ministry of Training, Colleges and Universities, Student Support Branch | Thunder Bay |
 | Ontario. Ministry of Transportation | Toronto |
 | Ontario. ServiceOntario. Publications Ontario | Toronto |
| | OPAL Self-help for Physically Challenged | Mitchell |
 | Optimism Place | Stratford |
| | Optimism Place, Dating Violence Prevention | Stratford |
 | Optimism Place, Early Intervention Program | Stratford |
| | Optimist International, Optimist Club of Avon River Club 46021 Zone 1 | Stratford |
| | Optimist International, Optimist Club of Downie, Club 46051 Zone 1 | St Marys |
| | Optimist International, Optimist Club of Ellice, Club 46069 Zone 1 | Rostock |
| | Optimist International, Optimist Club of Festival City (Stratford), Club 46085 Zone 1 | Stratford |
| | Optimist International, Optimist Club of Kirkton-Woodham Club 46113 Zone 3 | Perth South |
| | Optimist International, Optimist Club of Listowel, Club 46123 Zone 6 | Listowel |
| | Optimist International, Optimist Club of Mitchell, Club 46136 Zone 1 | Mitchell |
| | Optimist International, Optimist Club of Mornington, Club 46145 Zone 1 | Milverton |
| | Optimist International, Optimist Club of Seaforth & District, Club 46923 Zone 2 | Seaforth |
| | Optimist International, Optimist Club of Sebringville, Club 46204 Zone 1 | Sebringville |
| | Optimist International, Optimist Club of Shakespeare, Club 46203 Zone 1 | Shakespeare |
| | Optimist International, Optimist Club of St Marys, Club 46225 Zone 3 | St Marys |
 | Optimist International, Optimist Club of Stratford, Club 46220 Zone 1 | Stratford |
| | Optimum Childcare Nannies and Senior Care Givers Inc | Vancouver |
 | Organ Donation and Transplant Association Canada | Stratford |
 | Orr Chiropractic Professional Corporation | Stratford |
 | Ovarian Cancer Canada | Toronto |