| | Organization Name(s) | Located In |
 | Dain City Recreation and Activity Centre | Welland |
 | Dalhousie Yacht Club | Port Dalhousie |
 | Dalhousie Yacht Club, Summer Sailing Camp 2013 | Port Dalhousie |
 | Dave McMahon's Dog Training Academy | Niagara Falls |
 | Dave Neary Counselling & Psychotherapy | St Catharines |
 | David James and Associates Professional Counselling Services | Beamsville |
| | Dawn Shickluna (MA, MEd) Counselling and Consulting Services | St Catharines |
 | Day Care Centre, The, A Special Place | Beamsville |
 | Day Care Centre, The, A Special Place 2 | Beamsville |
 | Dell Lewis and Krall Home Health | Welland |
 | Design for A New Tomorrow | St Catharines |
 | Design for A New Tomorrow, Partner Assault Response Program (PAR), PAR | St Catharines |
| | Developmental Services System- Niagara | Thorold |
| | Diabetes Niagara Network | St Catharines |
 | Dingman-Nagy School of Ballet Arts | Niagara Falls |
 | directSmiles, Mobile Dental Hygiene Services | Oakville |
| | Distress Centre of Niagara Inc | St Catharines |
 | District School Board of Niagara | St Catharines |
 | District School Board of Niagara, Adult & Community Education | St Catharines |
 | District School Board of Niagara, Community Education Services, Lifetime Learning Centre, Adult Education | St Catharines |
 | District School Board of Niagara, Community Education Services, Transition to Employment (TTE) | St Catharines |
 | District School Board of Niagara, Elected Officials/Trustees, Niagara Region | St Catharines |
 | District School Board of Niagara, Literacy and Basic Skills, St Catharines, Education Centre | St Catharines |
 | District School Board of Niagara, Literacy and Basic Skills, St Catharines, Stokes Building | St Catharines |
 | District School Board of Niagara, Literacy and Basic Skills, Welland, Seaway Mall | Welland |
 | District School Board of Niagara, Niagara Adult Literacy for the Deaf | St Catharines |
| | District School Board of Niagara, Parenting and Family Literacy Centres (PFLC) | St Catharines |
 | District School Board of Niagara, Special Education Services | Niagara-on-the-Lake |
 | Doors Open Niagara | USA |
| | Down Syndrome Caring Parents, Niagara | Niagara Falls |
| | Downtown Beamsville Improvement Area | Beamsville |
 | Down-Under Wool | Niagara Falls |
 | Dr Bruce Rosenberg - Diabetic Foot Care | St Catharines |
 | Dr Chi Mun Wong Family Practice and Walk-in | St Catharines |
 | Dr Mitchell's Medical Walk-In Clinic and Fort Erie Foot Care Services | Fort Erie |
| | Dr Simon Williams, PhD, Registered Psychologist: Children and Adolescents | Queenston |
| | Dragon Boat Festival | St Catharines |
 | Dreams to Memories Foundation | Fort Erie |
| | Dressage Niagara | St Catharines |
 | DriveTest, Driver Examination Centre, St Catharines | St Catharines |
| | Ducks Unlimited, Niagara Falls Chapter | Niagara Falls |
 | Dunlop Drive Older Adult Centre, Recreation and Activity Centre | St Catharines |
 | Dying With Dignity Canada, Advance Directives (Living Wills) | Toronto (City of) |
| | Dyslexia Clinic Niagara, Multisensory Academic Therapy | Welland |