| Macaulay Tree House Day Nursery | Bracebridge |
| MacLaren Art Centre, Art Classes and Day Camps for Children and Youth | Barrie |
| MacLaren Art Centre | Barrie |
| MADD Canada, Mailing Address, Barrie Simcoe Chapter | Barrie |
| Making Change, Mailing Address | Barrie |
| Mama Earth Organics, Mailing Address | Toronto |
| Manito Shriner's Club | Clearview (Simcoe County) |
| Maplehill Wellness, Barrie, Foot Care | Barrie |
| Mapleview Community Church, Barrie | Barrie |
| March of Dimes Canada, Barrie - Bryne Dr, Brain Injury Services - Outreach Activity Groups in Simcoe County | Barrie |
| March of Dimes Canada, Collingwood, Assisted Living Services and Low Acuity Services - Community Support Services Program | Collingwood |
| March of Dimes Canada, Homemaking Services, Collingwood | Collingwood |
| March of Dimes Canada, Midland, Assisted Living Services and Low Acuity Services - Community Support Services Program | Midland |
| March of Dimes Canada, Midland, Homemaking Services | Midland |
| March of Dimes Canada (GTA) | Toronto |
| Mariposa House Hospice | Severn |
| Math3ma Academy | Barrie |
| Matthews House, Hospice Services - Our Residential Services | New Tecumseth |
| May Court Club of Barrie, Barrie | Barrie |
| May Court Club of Barrie, Barrie, May Court Shop | Barrie |
| McQuaig (Wendy), Orillia, Registered Psychotherapist | Orillia |
| Meadow Creek Montessori School, Barrie - Ferndale Dr N, Meadow Creek Montessori School - West | Barrie |
| Meadow Creek Montessori School, Shanty Bay, Meadow Creek Montessori School - The Bay | Oro-Medonte |
| Meals On Wheels, Alliston | New Tecumseth |
| Mediation Centre of Simcoe County and Muskoka, Barrie | Barrie |
| MedicAlert Foundation Canada | North York |
| Mermigis (Dr Lambros) Psychologist | Barrie |
| Mete (Laurie Ann), Foot Care Nurse | Springwater |
| Métis Nation of Ontario - Barrie Office, Barrie, Community Wellness Program | Barrie |
| Métis Nation of Ontario - Barrie Office, Barrie, Homeowner Supports - Emergency Repair Program | Barrie |
| Métis Nation of Ontario - Midland, Metis Healthy Babies, Healthy Children, Midland | Midland |
| Midhurst Tennis Club | Springwater |
| Midland Civitan Club, Midland | Midland |
| Midland Midwives By the Bay | Midland |
| Midland Midwives By the Bay, Georgian Bay Women's Clinic | Midland |
| Midland Mountainview Family Co-operative Inc, Midland, Midland Mountainview Family Co-operative | Midland |
| Midland Public Library | Midland |
| Midland, Town of., Midland - Dominion Ave, Municipal Office | Midland |
| Midland, Town of., Various locations, Warming and Cooling Centres for Extreme Weather Relief | Midland |
| Midland-Penetang District CERT, Colborne St | Penetanguishene |
| Midwives Nottawasaga | Collingwood |
| Mill Creek Care Centre, Long Term Care Facility | Barrie |
| Ministry of Natural Resources, Southern Region - Peterborough | Peterborough |
| Ministry of Natural Resources, Summer Jobs For Students, No physical address | Peterborough |
| Ministry of Tourism, Culture and Gaming and Ministry of Sport, Toronto | Toronto |
| Mirror (The) | Midland |
| Mission Thrift Store - Barrie | Barrie |
| Mobicare Advanced Foot Care, Mobile Service | Barrie |
| Mobile Soup Kitchen | Collingwood |
| Modern College of Hairstyling and Esthetics | Barrie |
| Mom's 4 Mom's Doula Services, No Physical Address | Oro-Medonte |
| Monarchist League Barrie Huronia Branch | |
| Mortgage Centre (The), Christmas Hamper Program | Collingwood |
| MS Canada | Toronto |
| MTM Conservation Association, Tiny Marsh Nature Centre, Tiny Marsh Provincial Wildlife Area | Tiny |
| Mulcaster Mews Retirement Home, Mulcaster Mews | Barrie |
| MultiSport Canada | Barrie |
| Murray's Windermere Gardens | Barrie |
| Muscular Dystrophy Canada - Ontario Regional Office | North York |
| Museum on the Boyne | New Tecumseth |
| Music Therapy Services of Simcoe County, Barrie | Barrie |
| Muskoka Ambulance Communications Service | Bracebridge |
| Muskoka Drug Strategy Coalition | Gravenhurst |
| Muskoka Lakes Preschool | Muskoka Lakes Township |
| My Friend's House, Domestic Violence Shelter | Collingwood |
| My Pre Academy | Barrie |
| My Sister's Place | New Tecumseth |