| Oak Valley Health | Hospitals & Boards of Public Health | 2025 | 726 | $123,269 |
| Oakmed Family Health Team | Other Public Sector Employers | 2023 | 1 | $122,200 |
| Oaks Revitalization Association | Other Public Sector Employers | 2025 | 3 | $143,333 |
| Oakville - Trafalgar Memorial Hospital | Hospitals & Boards of Public Health | 1998 | 1 | $118,627 |
| Oakville Public Library | Municipalities & Services | 2005 | 1 | $111,749 |
| Oakville Public Library Board | Municipalities & Services | 2009 | 3 | $110,471 |
| Oakville Senior Citizens Residence | Other Public Sector Employers | 2025 | 4 | $139,427 |
| Oasis Addiction Recovery Society | Other Public Sector Employers | 2024 | 2 | $102,202 |
| Oasis Centre des Femmes | Other Public Sector Employers | 2025 | 1 | $152,835 |
| Oasw (Ontario Association of Social Workers) | Other Public Sector Employers | 2018 | 1 | $132,663 |
| OCASI-Ontario Council of Agencies Serving Immigrants | Other Public Sector Employers | 2021 | 2 | $125,433 |
| Occupational Health Clinics for Ontario Workers Inc | Other Public Sector Employers | 2025 | 32 | $123,042 |
| OCETA | Crown Agencies | 1996 | 2 | $125,000 |
| OCSTA Ontario Catholic School Trustees' Association | Other Public Sector Employers | 2015 | 2 | $134,878 |
| Oecm (Ontario Education Collaborative Marketplace) | Other Public Sector Employers | 2017 | 6 | $150,753 |
| OEPSC | Crown Agencies | 2001 | 10 | $218,077 |
| Office for Victims of Crime | Crown Agencies | 2016 | 1 | $123,575 |
| Office of the Auditor General | Government of Ontario – Legislative Assembly and Offices | 2025 | 94 | $155,653 |
| Office of the Chair (Ontario Parole & Earned Release Board) | Crown Agencies | 2009 | 4 | $126,230 |
| Office of the Chief Election Officer | Government of Ontario – Ministries | 1999 | 1 | $118,912 |
| Office of the Chief Electoral Officer | Government of Ontario – Legislative Assembly and Offices | 2025 | 102 | $141,247 |
| Office of the Conflict of Interest Commissioner | Crown Agencies | 2019 | 1 | $121,316 |
| Office of the Employer Adviser | Crown Agencies | 2025 | 15 | $132,056 |
| Office of the Employer Advisor | Crown Agencies | 2009 | 1 | $190,138 |
| Office of the Fairness Commissioner | Crown Agencies | 2025 | 5 | $142,454 |
| Office of the French Language Services Commissioner | Crown Agencies | 2013 | 1 | $167,076 |
| Office of the Premier | Government of Ontario – Ministries | 2025 | 50 | $162,895 |
| Office of the Worker Adviser | Crown Agencies | 2025 | 35 | $123,403 |
| Office, télécomm. éduc. de langue française de l'Ontario | Crown Agencies | 2008 | 5 | $145,074 |
| OHTB | Crown Agencies | 2000 | 1 | $111,865 |
| Ojibways of Onigaming | Other Public Sector Employers | 2016 | 1 | $102,750 |
| Ojibways of Onigaming First Nation | Other Public Sector Employers | 2025 | 3 | $105,825 |
| Olde Forge Community Resource Centre | Other Public Sector Employers | 2025 | 1 | $106,197 |
| Older Adult Centres Association of Ontario (OACAO) | Other Public Sector Employers | 2025 | 1 | $112,348 |
| OMB | Crown Agencies | 2000 | 2 | $158,606 |
| Ombudsman Ontario | Government of Ontario – Legislative Assembly and Offices | 2025 | 122 | $135,003 |
| OMEIFA | Crown Agencies | 2003 | 3 | $127,973 |
| OMERS Administration Corporation | Crown Agencies | 2008 | 150 | $208,732 |
| OMERS Sponsors Corporation | Other Public Sector Employers | 2008 | 1 | $163,384 |
| On Track Career and Employment Services Inc | Other Public Sector Employers | 2017 | 2 | $160,558 |
| On-Track Career and Employment Services | Other Public Sector Employers | 2014 | 1 | $120,719 |
| One Bowl Housing Corporation | Other Public Sector Employers | 2025 | 1 | $147,631 |
| One Care Home and Community Support Services | Other Public Sector Employers | 2025 | 5 | $123,902 |
| One Change Foundation | Other Public Sector Employers | 2010 | 2 | $125,769 |
| One Kids Place | Other Public Sector Employers | 2008 | 1 | $117,459 |
| One Kids Place Children's Med. Treat. Ctr., Northeast Ont. | Other Public Sector Employers | 2010 | 1 | $136,379 |
| One Kids Place Children's Medical Treatment Centre of North East Ontario | Other Public Sector Employers | 2025 | 6 | $131,886 |
| One Kids Place Children's Medical Treatment Centre of Northeast Ontario | Other Public Sector Employers | 2016 | 3 | $110,172 |
| Oneida Nation of the Thames | Other Public Sector Employers | 2025 | 8 | $110,978 |
| Ongwanada | Other Public Sector Employers | 2003 | 1 | $161,366 |
| Ongwanada Hospital | Other Public Sector Employers | 2025 | 20 | $125,561 |
| Ongwanada Hospital (Community Centre) | Other Public Sector Employers | 2006 | 2 | $146,016 |
| Ongwanada Resource Centre | Other Public Sector Employers | 1998 | 1 | $118,664 |
| Onkwehon:We Midwives Collective | Other Public Sector Employers | 2020 | 1 | $195,229 |
| Ont. Assoc'n of Children's Aid Societies | Other Public Sector Employers | 2005 | 4 | $113,476 |
| Ont. Assoc. of Children's Aid Soc. | Other Public Sector Employers | 2002 | 1 | $141,821 |
| Ont. Assoc. of Children's Aid Societies | Other Public Sector Employers | 1997 | 1 | $121,461 |
| Ont. Assoc. of Comm. Care Access Ctrs. | Other Public Sector Employers | 2005 | 1 | $154,363 |
| Ont. Association of Children's Aid Soc. | Other Public Sector Employers | 2003 | 1 | $146,650 |
| Ont. Civilian Comm. on Police Services | Crown Agencies | 2005 | 2 | $141,600 |
| Ont. Civilian Comm. on Police Srvcs. | Crown Agencies | 2004 | 1 | $167,668 |
| Ont. Civilian Commission on Police Services | Crown Agencies | 2003 | 1 | $173,982 |
| Ont. Council of Regents | Crown Agencies | 1997 | 1 | $109,262 |
| Ont. Dairy Herd Improvement | Other Public Sector Employers | 2003 | 3 | $127,757 |
| Ont. Farm Products Marketing Comm. | Crown Agencies | 2004 | 2 | $128,533 |
| Ont. Farm Products Marketing Commission | Crown Agencies | 2003 | 1 | $152,028 |
| Ont. Fed'n. of Indian Friendship Ctr. | Other Public Sector Employers | 2005 | 1 | $124,758 |
| Ont. Fed'n. of Indian Friendship Ctrs. | Other Public Sector Employers | 2004 | 1 | $122,603 |
| Ont. Flue-Cured Tobacco Growers Board | Other Public Sector Employers | 2005 | 1 | $122,225 |
| Ont. HIV Treatment Network | Other Public Sector Employers | 2005 | 1 | $132,605 |
| Ont. Legal Aid Plan | Other Public Sector Employers | 1997 | 5 | $113,921 |
| Ont. Municipal Board | Crown Agencies | 1997 | 1 | $115,000 |
| Ont. Northland Transport. Comm. | Crown Agencies | 1997 | 5 | $118,693 |
| Ont. Parole & Earned Release Board | Crown Agencies | 2004 | 1 | $119,836 |
| Ont. Physical & Hlth. Ed. Association | Other Public Sector Employers | 2005 | 1 | $112,461 |
| Ont. Problem Gambling Research Centre | Other Public Sector Employers | 2003 | 1 | $119,100 |
| Ont. Problem Gambling Research Ctr. | Other Public Sector Employers | 2004 | 1 | $125,054 |
| Ont. Secretariat for Aboriginal Affairs | Government of Ontario – Ministries | 2005 | 4 | $113,880 |
| Ont. Swine Improvement Inc. | Crown Agencies | 1997 | 1 | $107,211 |
| Ont. Tourism Marketing Partnership | Crown Agencies | 2004 | 3 | $117,586 |
| Ont. Trsm Mrktng Prtnrshp Corp. | Crown Agencies | 2000 | 1 | $117,927 |
| Ont.Civillian Comm. on Police Srvcs | Crown Agencies | 2002 | 1 | $164,716 |
| Ont.Farm Products Marketing Comm. | Crown Agencies | 2002 | 1 | $135,498 |
| Ontario 211 Services Corp. | Other Public Sector Employers | 2010 | 1 | $137,915 |
| Ontario 211 Services Corporation | Other Public Sector Employers | 2025 | 1 | $163,873 |
| Ontario Aboriginal HIV/AIDS Strategy | Other Public Sector Employers | 2025 | 1 | $116,151 |
| Ontario Aboriginal Housing | Other Public Sector Employers | 2011 | 1 | $134,922 |
| Ontario Aboriginal Housing Support Services Corporation | Other Public Sector Employers | 2025 | 10 | $131,925 |
| Ontario Agency for Health Protection and Promotion | Crown Agencies | 2025 | 318 | $137,960 |
| Ontario Agri-Food Education Inc | Other Public Sector Employers | 2024 | 1 | $105,000 |
| Ontario Agri-Food Technologies | Other Public Sector Employers | 2017 | 1 | $165,083 |
| Ontario AIDS Network | Other Public Sector Employers | 2025 | 2 | $120,980 |
| Ontario Artistic Swimming | Other Public Sector Employers | 2025 | 1 | $110,000 |
| Ontario Arts Council | Crown Agencies | 2025 | 28 | $131,592 |
| Ontario Assn. of Children's Aid Soc. | Other Public Sector Employers | 1998 | 1 | $127,048 |
| Ontario Association for Family Mediation | Other Public Sector Employers | 2025 | 1 | $104,000 |
| Ontario Association of Adult and Continuing Education School Board Administrators (CESBA) | Other Public Sector Employers | 2025 | 2 | $107,100 |
| Ontario Association of Adult and Continuing Education Schoolboard Administrators | Other Public Sector Employers | 2015 | 1 | $104,503 |
| Ontario Association of Chiefs of Police (OACP) | Other Public Sector Employers | 2025 | 3 | $147,029 |
| Ontario Association of Children's Aid Societies (OACAS) | Other Public Sector Employers | 2025 | 28 | $125,890 |