| D&K Footcare Services | Bradford West Gwillimbury |
| Danube Seniors Leisure Centre | Bradford West Gwillimbury |
| Deaf Access Simcoe Muskoka, Barrie Central Office, American Sign Language Classes | Barrie |
| Deaf Access Simcoe Muskoka, Barrie Central Office, American Sign Language Interpreting | Barrie |
| Deaf Access Simcoe Muskoka, Barrie Central Office, Community Support Services | Barrie |
| Deaf Access Simcoe Muskoka, Barrie Central Office | Barrie |
| Deaf Access Simcoe Muskoka, Barrie Central Office, Employment Services | Barrie |
| DeafBlind Ontario Services | Newmarket |
| Dietitians of Canada - UnlockFood.ca | Toronto Downtown Central |
| Discovery Harbour, Penetanguishene | Penetanguishene |
| Distance Education. Ontario Colleges of Applied Arts and Technology | Ontario |
| Doane House Hospice | Newmarket |
| Down Syndrome Association of Simcoe County, Mailing Address | Barrie |
| Dr. Dianne Maing Psychologist, Barrie | Barrie |
| Dragon Boat Barrie (Ontario), Mailing Address | Barrie |
| DriveTest / Serco Des | Barrie |
| Drysdale's Tree Farm | Essa |
| Dufferin Simcoe Land Stewardship Network | Mulmur |
| Dufferin, County of, Orangeville - Edelbrock Centre, Employment Resource Centres | Orangeville |
| Dying with Dignity Canada | Toronto |
| Dynamic Neurophysiotherapy, Mobile Service, Mobile Physiotherapy | Barrie |