| Ontario Womens Directorate | Government of Ontario – Ministries | 1999 | 1 | $113,058 |
| Ontario Éducation Collaborative Marketplace | Other Public Sector Employers | 2015 | 6 | $136,350 |
| Ontario's Highlands Tourism Organization | Other Public Sector Employers | 2025 | 1 | $118,535 |
| OntarioMD Inc. | Other Public Sector Employers | 2011 | 36 | $132,977 |
| OnTrace Agri-food Traceability | Other Public Sector Employers | 2011 | 2 | $200,039 |
| Ontrack Career and Employment Services Inc. | Other Public Sector Employers | 2015 | 1 | $118,000 |
| On–Trace Agri–Food Traceability Incorporated | Other Public Sector Employers | 2012 | 1 | $214,794 |
| Oolagen Community Services | Other Public Sector Employers | 2015 | 1 | $134,585 |
| OPCMIA Local 598 Training Centre | Other Public Sector Employers | 2025 | 3 | $108,009 |
| Open Doors for Lanark Children & Youth | Other Public Sector Employers | 2013 | 1 | $102,496 |
| Open Doors for Lanark Children and Youth | Other Public Sector Employers | 2024 | 1 | $143,419 |
| Open Hxouse Inc | Other Public Sector Employers | 2025 | 1 | $150,000 |
| Operation Come Home | Other Public Sector Employers | 2023 | 1 | $107,500 |
| Operation Springboard | Other Public Sector Employers | 2025 | 4 | $145,080 |
| Ophea | Other Public Sector Employers | 2018 | 1 | $158,330 |
| Opportunity for Advancement | Other Public Sector Employers | 2025 | 1 | $110,252 |
| Optical Reg. Advanced Network of Ont. | Other Public Sector Employers | 2002 | 1 | $112,712 |
| Optical Reg. Advanced Network, Ont. | Other Public Sector Employers | 2003 | 1 | $120,000 |
| Optical Regional Advanced Network Ont. | Other Public Sector Employers | 2005 | 2 | $131,400 |
| Options Northwest Personal Support Services | Other Public Sector Employers | 2025 | 4 | $112,928 |
| Organization of Canadian Nuclear Industries (OCI) | Other Public Sector Employers | 2021 | 1 | $201,630 |
| Orillia Soldiers Memorial Hospital | Hospitals & Boards of Public Health | 2025 | 366 | $122,658 |
| Orion | Other Public Sector Employers | 2019 | 13 | $176,902 |
| Orleans-Cumberland Community Resource Centre Centre de Ressources Communautaires Orleans-Cumberland | Other Public Sector Employers | 2017 | 1 | $119,342 |
| Orleans–Cumberland Community Resource Centre / Centre de ressources communautaires Orléans–Cumberland | Other Public Sector Employers | 2012 | 1 | $120,790 |
| Orléans-Cumberland Community Resource Centre | Other Public Sector Employers | 2016 | 1 | $128,522 |
| ORNGE | Other Public Sector Employers | 2025 | 406 | $146,760 |
| ORTECH Corporation | Crown Agencies | 1998 | 5 | $146,493 |
| Orthopaedic & Arthritic Hospital | Hospitals & Boards of Public Health | 1996 | 1 | $126,403 |
| Osgoode Care Centre | Other Public Sector Employers | 2025 | 11 | $127,103 |
| Oshawa Clarington Assoc. Com. Liv. | Other Public Sector Employers | 2002 | 1 | $101,237 |
| Oshawa Community Health Centre | Other Public Sector Employers | 2015 | 4 | $237,476 |
| Oshawa General Hospital | Hospitals & Boards of Public Health | 1997 | 2 | $132,676 |
| Oshawa Public Library | Other Public Sector Employers | 2017 | 3 | $125,609 |
| Oshawa Public Library Board | Other Public Sector Employers | 2015 | 3 | $114,662 |
| Oshawa Senior Citizens Centre | Other Public Sector Employers | 2025 | 9 | $127,504 |
| Oshawa Young Women's Christian Association | Other Public Sector Employers | 2025 | 1 | $153,686 |
| Oshawa/Clarington Community Living | Other Public Sector Employers | 2004 | 1 | $119,390 |
| Oshki-Pimache-O-Win Education and Training Institute | Other Public Sector Employers | 2018 | 1 | $100,299 |
| Oshki-pimache-o-win: the Wenjack Education Institute | Other Public Sector Employers | 2025 | 1 | $102,629 |
| OSIFA | Crown Agencies | 2005 | 4 | $149,923 |
| Osstf/Feeso Provincial Health Benefit Plan Corporation | Other Public Sector Employers | 2016 | 1 | $112,500 |
| Osteoporosis Canada | Other Public Sector Employers | 2025 | 5 | $148,083 |
| Osteoporosis Society of Canada | Other Public Sector Employers | 2018 | 5 | $137,296 |
| Otonabee Region Conservation Authority | Other Public Sector Employers | 2019 | 1 | $111,459 |
| Ottawa Bluesfest | Other Public Sector Employers | 2021 | 1 | $103,641 |
| Ottawa Board of Education | School Boards | 1997 | 4 | $116,104 |
| Ottawa Carleton Association for Persons with Developmental Disabilities | Other Public Sector Employers | 2016 | 3 | $121,273 |
| Ottawa Carleton Cd EP | School Boards | 1997 | 1 | $106,693 |
| Ottawa Carleton CSCdD | School Boards | 1997 | 1 | $118,041 |
| Ottawa Carleton Lifeskills | Other Public Sector Employers | 2013 | 1 | $100,881 |
| Ottawa Carleton Lifeskills Inc | Other Public Sector Employers | 2025 | 6 | $125,639 |
| Ottawa Catholic School Board | School Boards | 2025 | 2,495 | $124,058 |
| Ottawa CCAC | Other Public Sector Employers | 2002 | 3 | $123,138 |
| Ottawa Centre for Regional Innovation | Other Public Sector Employers | 2015 | 1 | $262,870 |
| Ottawa Centre for Research & Innovation | Other Public Sector Employers | 2010 | 3 | $150,617 |
| Ottawa Child. Treatment Ctr. | School Boards | 2003 | 1 | $119,711 |
| Ottawa Children's Treatment Centre | Other Public Sector Employers | 2015 | 14 | $126,899 |
| Ottawa Chinese Community Service Centre | Other Public Sector Employers | 2019 | 1 | $108,487 |
| Ottawa Civic Hospital | Hospitals & Boards of Public Health | 1997 | 16 | $150,921 |
| Ottawa Community Housing Corporation | Other Public Sector Employers | 2025 | 124 | $130,838 |
| Ottawa Community Immigrant Services Organization | Other Public Sector Employers | 2017 | 1 | $116,373 |
| Ottawa Congress Centre | Crown Agencies | 2007 | 3 | $117,619 |
| Ottawa Convention Centre Corporation | Crown Agencies | 2025 | 8 | $167,081 |
| Ottawa Dragon Boat Race Festival | Other Public Sector Employers | 2019 | 1 | $112,341 |
| Ottawa Foyers Partage | Other Public Sector Employers | 2025 | 3 | $120,791 |
| Ottawa General Hospital | Hospitals & Boards of Public Health | 1997 | 15 | $148,704 |
| Ottawa Health Research Institute | Hospitals & Boards of Public Health | 2006 | 13 | $133,824 |
| Ottawa Hospital | Hospitals & Boards of Public Health | 2025 | 3,195 | $122,504 |
| Ottawa Hospital Research Institute | Other Public Sector Employers | 2025 | 154 | $146,609 |
| Ottawa Inner City Health Inc | Other Public Sector Employers | 2025 | 15 | $127,709 |
| Ottawa Inuit Children's Centre | Other Public Sector Employers | 2018 | 1 | $119,011 |
| Ottawa Jazz | Other Public Sector Employers | 2021 | 1 | $101,920 |
| Ottawa Jewish Home for the Aged - Hillel Lodge | Other Public Sector Employers | 2011 | 1 | $106,000 |
| Ottawa Network for Education | Other Public Sector Employers | 2025 | 2 | $140,911 |
| Ottawa Network for Education/ Reseau D' Ottawa Pour l'Education | Other Public Sector Employers | 2017 | 1 | $124,000 |
| Ottawa Public Library | Other Public Sector Employers | 2000 | 1 | $109,462 |
| Ottawa R.C.S.S.B. | School Boards | 1996 | 1 | $109,733 |
| Ottawa Rape Crisis Centre | Other Public Sector Employers | 2025 | 2 | $112,858 |
| Ottawa Roman Catholic Separate School Board | School Boards | 1996 | 1 | $120,661 |
| Ottawa Rotary Home | Other Public Sector Employers | 2025 | 2 | $115,556 |
| Ottawa Salus Corp | Other Public Sector Employers | 2025 | 4 | $132,425 |
| Ottawa Salus Corporation | Other Public Sector Employers | 2015 | 1 | $110,298 |
| Ottawa Tourism and Convention Authority Inc | Other Public Sector Employers | 2022 | 8 | $146,817 |
| Ottawa Transportation | Other Public Sector Employers | 2000 | 8 | $112,012 |
| Ottawa Valley Family Health Team | Other Public Sector Employers | 2023 | 3 | $116,059 |
| Ottawa Victim Services | Other Public Sector Employers | 2025 | 1 | $101,661 |
| Ottawa Walls and Ceilings Training Centre | Other Public Sector Employers | 2025 | 1 | $109,982 |
| Ottawa West Community Support | Other Public Sector Employers | 2025 | 2 | $132,251 |
| Ottawa Young Men's and Young Women's Christian Assoc | Other Public Sector Employers | 2025 | 12 | $151,126 |
| Ottawa-Carleton Assn. for Persons w/Develop'l Disabilities | Other Public Sector Employers | 2010 | 1 | $133,708 |
| Ottawa-Carleton Assoc Persons w/Dev Dis | Other Public Sector Employers | 2005 | 1 | $106,600 |
| Ottawa-Carleton Assoc. for Persons with Dev. Disabilities | Other Public Sector Employers | 2007 | 1 | $109,800 |
| Ottawa-Carleton Assoc. for Persons with Devel. Disabilities | Other Public Sector Employers | 2006 | 1 | $108,750 |
| Ottawa-Carleton Association for Persons With Developmental Disabilities (OCAPDD) | Other Public Sector Employers | 2025 | 8 | $129,368 |
| Ottawa-Carleton CCAC | Other Public Sector Employers | 2000 | 1 | $125,645 |
| Ottawa-Carleton Children's Aid Soc. | Other Public Sector Employers | 1998 | 1 | $125,490 |
| Ottawa-Carleton Citizen Advocacy Parrainage Civique d'O/C | Other Public Sector Employers | 2017 | 1 | $100,062 |
| Ottawa-Carleton District Sch Bd | School Boards | 1998 | 1 | $102,582 |
| Ottawa-Carleton District School Board | School Boards | 2025 | 3,847 | $120,487 |