| D&K Footcare Services | Bradford West Gwillimbury |
| Daisy A Day Home Care, Barrie | Barrie |
| Dancers Studio (The) | Midland |
| Danube Seniors Leisure Centre | Bradford West Gwillimbury |
| Daughters of Isabella, Penetanguishene, Daughters of Isabella - Penetanguishene | Penetanguishene |
| Days For Girls, No Physical Address, Days For Girls Barrie | Barrie |
| 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 |
| Defined Spaces | Bracebridge |
| Delta Health Clinics, Barrie - Grove St E, Opioid Addiction / Dependence Treatment | Barrie |
| Delta Health Clinics, Barrie - Leacock Dr, Opioid Addiction / Dependence Treatment | Barrie |
| Delta Health Clinics, Barrie - Wellington St W, Opioid Addiction / Dependence Treatment | Barrie |
| Developmental Services Ontario Central East Region, York Support Services Network - Central East Region, Your Support Services Network - Central East Region | Aurora |
| Developmental Services Ontario, Central East Region, Aurora Office | Aurora |
| Diabetes Canada | Toronto Downtown Central |
| Diabetes Canada, D-Camps Ontario | Huntsville |
| Dietitians of Canada | Toronto Downtown Central |
| Dietitians of Canada - UnlockFood.ca | Toronto Downtown Central |
| Discovery Child Care Centre, Barrie - Thrushwood Dr, Child Care Centre | Barrie |
| Discovery Harbour, Penetanguishene | Penetanguishene |
| Distance Education. Ontario Colleges of Applied Arts and Technology | Ontario |
| Divine Landscape, Mobile Service, WasagaSnow.ca | Wasaga Beach |
| Doane House Hospice | Newmarket |
| Donaven Renovations, Lawn Care and Snow Blowing, Mobile Service | Wasaga Beach |
| Dorvict Home and Health Care Services, Barrie | Barrie |
| Doug's Home and Lawn Care, Mailing address | Wasaga Beach |
| Doula Group (The) | Barrie |
| Doula Services, Labour and Delivery Support | Midland |
| Down Syndrome Association of Simcoe County, Mailing Address | Barrie |
| Downtown Barrie BIA, Barrie | Barrie |
| Downtown Midland Business Improvement Area | Midland |
| Downtown Orillia Management Board | Orillia |
| Dr. Dianne Maing Psychologist, Barrie | Barrie |
| Dragon Boat Barrie (Ontario), Mailing Address | Barrie |
| Drayton Entertainment, King's Wharf Theatre | Penetanguishene |
| Dress for Success, Barrie | Barrie |
| Driverseat | Barrie |
| DriveTest, Collingwood, Driver Examination Centre, Collingwood | Collingwood |
| DriveTest, Orillia, Driver Examination Centre | Orillia |
| DriveTest / Serco Des | Barrie |
| DriveTest / Serco Des, Barrie, Driver Examination Centre | Barrie |
| D-tek-TION Security Systems, Mobile Service | Barrie |
| Ducks Unlimited Canada, Barrie | Barrie |
| Dufferin Simcoe Land Stewardship Network | Mulmur |
| Duntroon Day Care | |
| Dying with Dignity Canada | Toronto |
| Dynacare Medical Laboratory, Huronia Medical Centre Laboratory | Midland |
| Dynamic Neurophysiotherapy, Mobile Service, Mobile Physiotherapy | Barrie |