| A Cappella Showcase | Waterdown |
| A+ Medical Centre and Walk-In | Milton |
| Abbey Oaks Slo Pitch, Men's Slo Pitch League | Oakville |
| Abbeywood Pharmacy, Pharmacy Services | Oakville |
| ABC Health Transportation | Milton |
| Ability Clinic (The) | Dixie |
| Ability Concepts | Mississauga |
| AbleLiving Services, Burlington - Westwood Hub, Community Outreach Services | Burlington |
| AbleLiving Services, Burlington - Bethany Residence, Supportive Housing | Burlington |
| AbleLiving Services, Burlington - Palmer Place, Supportive Housing | Burlington |
| Access Abilities, Medical Equipment Retailer | Oakville |
| Access Dental Care, Mobile Dental Hygiene Service | Mississauga |
| Access Personal Support, In Home Care Services | Burlington |
| Acclaim Health, Friendly Visiting / Memory Visiting | Oakville |
| Acclaim Health, Home Care | Oakville |
| Acclaim Health, Technology Accessibility Program | Oakville |
| Acclaim Health, Tele-Touch | Oakville |
| Acclaim Health, Burlington - Fairview St, Foot Care | Burlington |
| Acclaim Health, Burlington - Itabashi Way, Adult Day Program | Burlington |
| Acclaim Health, Mississauga Club, Adult Day Program | Mississauga |
| Acclaim Health, Community Support Services | Oakville |
| Acclaim Health, Home Support Exercise Program | Halton Region |
| Acclaim Health, Hospice Care and Bereavement Support | Oakville |
| Acclaim Health, Palliative Care Consultation | Oakville |
| Acclaim Health, Caregiver Education and Support | Oakville |
| Acclaim Health, JIM's Suites - Overnight Respite | Oakville |
| Acclaim Health, Patty's Place - Dementia Care Centre | Oakville |
| Acclaim Health, Soper Club - Adult Day Program | Oakville |
| Acclaim Health, Walmley Club - Adult Day Program | Oakville |
| Active Aldershot Society | Burlington |
| Acton Agricultural Society | Acton |
| Acton Aqua Ducks Swim Club | Acton |
| Acton Badminton Club, Recreational Badminton | Acton |
| Acton Citizens Band | Acton |
| Acton Curling Club | Acton |
| Acton Foodshare, Food Bank | Acton |
| Acton Horticultural Society | Acton |
| Acton Medical and Urgent Care | Halton Hills |
| Acton Skating Club | Acton |
| Acton Soccer Club | Acton |
| Acton-Halton Walk-in Clinic | Halton Hills |
| ADAPT Halton, Oakville - Head Office, Alcohol, Drug and Gambling Assessment, Prevention and Treatment Services | Oakville |
| ADAPT Halton, Burlington Office | Burlington |
| ADAPT Halton, Community Withdrawal Management Services | Halton Region |
| ADAPT Halton, Concurrent Disorders Programs | Halton Region |
| ADAPT Halton, Georgetown Office | Georgetown |
| ADAPT Halton, Milton Office | Milton |
| ADAPT Halton, Problem Gambling & Behavioural Addictions Services | Halton Region |
| Adaptive Clothing, Halton Region | Ontario |
| Adoption Council of Ontario, Markham - Mailing Address | Markham |
| Adult Recreational League | Burlington |
| Adults in Motion, Day Program | Oakville |
| Advocacy Centre for the Elderly | Toronto |
| Afghan Association of Ontario, Canada | Toronto |
| African Caribbean Council of Halton | Milton |
| African Community Services of Peel, Brampton, Family Program | Brampton |
| African Community Services of Peel, Brampton, Violence Against Women Program | Brampton |
| Age Wisely Senior Care, In-Home Care Services | Mississauga |
| AgeCare Brant, Long Term Care Home | Burlington |
| AgeCare Glen Oaks, Long Term Care Residence | Oakville |
| Akwaba Cultural Exchange, Cultural Heritage Group | Milton |
| Al-Anon Family Groups, Halton Hills and Milton, Al-Anon and Alateen Meetings | Halton Hills |
| Al-Anon Family Groups, Hamilton / Burlington, Al-Anon / Alateen Meetings | Burlington |
| Al-Anon Family Groups, Oakville, Al-Anon / Alateen Meetings | Oakville |
| Alcoholics Anonymous, Oakville - Halton District Office, Halton Area Meetings | Halton Region |
| Alcoholics Anonymous - North Halton/Erin, North Halton / Erin District, Erin and Area Meetings | Erin |
| Alcoholics Anonymous (GTA), Find an Alcoholics Anonymous Meeting - Greater Toronto Area Intergroup | Ontario |
| Alcoholics Anonymous Hamilton, Alcoholics Anonymous Meetings | |
| Aldershot Community Recreation Association | Burlington |
| Aldershot Tennis Club | Burlington |
| ALEPHCARE, In-Home Care Services | Mississauga |
| Allendale Volunteers | Milton |
| Alpha Care Medical Center, Family Practice and Walk-in | Georgetown |
| Alpha Care Pharmacy, Pharmacy Services | Halton Hills |
| ALS Canada | Toronto Downtown North |
| Always Best Care Senior Services, In-Home Care Services | Oakville |
| Alzheimer Society of Brant, Haldimand Norfolk, Hamilton Halton, Halton Office | Burlington |
| Alzheimer Society of Brant, Haldimand Norfolk, Hamilton Halton, Burlington Locations, Exercise Classes | Burlington |
| Alzheimer Society Peel | Port Credit |
| Alzheimer Society Peel, First Link | Mississauga |
| Alzheimer Society Peel, Mississauga - Main Office, Behavioural Supports Ontario (BSO) | Port Credit |
| Alzheimer Society Peel, Dementia Resources Consulting and Support Groups | Port Credit |
| American Women's Club of Southern Ontario, Social Club | Oakville |
| Amica Bronte Harbour, Retirement Residence | Oakville |
| Amica Senior Lifestyles, Georgetown, Retirement Residence | Halton Hills |
| Angels My Way Home Care | Oakville |
| Anglican Church of the Incarnation | Oakville |
| Appleby Pharmacy, Pharmacy Services | Burlington |
| Appleby Tennis Club | Burlington |
| Appleby United Church | Burlington |
| Arcavia Home Care, In Home Care Services | Oakville |
| ARCH Disability Law Centre, Community legal clinic | Toronto |
| Armenian Family Support Services | Toronto |
| Art Gallery of Burlington | Burlington |
| Arthritis Society Canada, Burlington, Hamilton & Niagara Region Office, Community Support | Burlington |
| Arthritis Society Canada, Halton East and Peel Region, Mississauga | Mississauga |
| Arts Burlington | Burlington |
| Arts Milton | Milton |
| ArtWorks Oakville | Oakville |
| Aspira Retirement Living, Milton - Martindale Gardens, Retirement Residence | Milton |
| Assaulted Women's Helpline | |
| Assaulted Women's Helpline, Seniors Safety Line | |
| Assisted Mobility Solutions | Georgetown |
| Asthma Canada | Toronto Downtown North |
| Autism Ontario, Halton Chapter - Mailing Address | Burlington |
| Avanti Homecare, In Home Care Services | Milton |
| Avella Injury and Pain Management, Pain Management Services | Burlington |
