| Name | Phone | Category |
| D&D Consulting and Training | 240-688-8888 | Accountants/CPA's |
| Dale Carnegie Training | (717) 540-0801 | Education/Training |
| Dallavalle & Company P.A. | (301) 695-0645 | Accountants/CPA's |
| Damascus Road Community Church | 301-253-5276 | Church/Synagogue |
| Danielle's Italian & American Cuisine | (301) 663-6600 | Restaurants/Cafes |
| Dave's Lock and Key LLC | (240) 674-7564 | Locksmith |
| Dawn Cramer Stein, CPA | (301) 663-8368 | Accountants/CPA's |
| Days End Farm Horse Rescue, Inc. | 301-520-7467 | Non-Profit Organizations |
| DeHavilland Properties | (301) 694-3120 | Commercial Real Estate |
| DeLauder Insurance Agency, LLC | (301) 694-0028 | Insurance Agencies/ Brokers |
| Delegate Charles A. Jenkins | | Government Agencies |
| Delegate Donald Elliott | 410-841-3118 | Government Agencies |
| Delegate Galen Clagett | 410-841-3436 | Government Agencies |
| Delegate Joseph R. Bartlett | 410-841-3080 | Government Agencies |
| Delegate Paul Stull | 410-841-3288 | Government Agencies |
| Delegate Sue Hecht | 301-662-2464 | Government Agencies |
| Detterline Orthodontics | 301-831-3900 | Orthodontics |
| Dewberry | (301) 663-3158 | Engineering Services |
| Digital Bard Video | 240-566-5931 | Audio/Video Production |
| Dillon Lightning Protection Systems, Inc. | 301-696-9027 | |
| Diversified Auto Tag & Title Services | 301-378-0900 | Automotive Services |
| Division of Rehabilitation Services | (301) 600-3075 | Employment Services |
| Donald B. Rice Tire Co. | (301) 662-0166 | Automotive |
| Donna Kaye Personnel/Spherion | (301) 694-7700 | Employment Services |
| Douglas Development Corporation | (202) 638-6300 | Developers |
| Downtown Frederick Partnership | (301) 698-8118 | Non-Profit Organizations |
| Downtown New Market Partnership | | Non-Profit Organizations |
| Downtown Piano Works | 301-631-1234 | Retailers |
| Draper & McGinley, P.A. | (301) 694-7411 | Accountants/CPA's |
| Dutch's Daughter, Inc. | (301) 668-9500 | Restaurants/Cafes |
| DynPort Vaccine Company LLC | (301) 607-5000 | Biomedical/ Biotechnology |