| Name | Phone | Category |
| A Corner Office LLC | 301-696-5701 | Office Rentals |
| A Cut Above Catering | 301-663-1516 | Caterers |
| Ability Prosthetics & Orthotics, Inc. | (717) 337-2273 | Health Services |
| Acacia Fusion Bistro | (301) 694-3015 | Restaurants/Cafes |
| Acela Technologies, Inc. | (301) 846-9060 | Information Technology |
| Adams County Winery | 717-334-4631 | Winery |
| Adecco Employment Services | (301) 631-9000 | Employment Services |
| Advance Business Systems | (301) 694-6662 | Office Equipment/Supplies |
| Advanced Helicopter Youth Foundation | 301-351-5640 | Non-Profit Organizations |
| Advanced Urgent Care of Frederick | (240) 379-7776 | Health Services/Doctors Offices |
| Adventist Health Care-Germantown | (301) 315-3042 | Health Services |
| Adventure Park USA | (301) 865-6800 | Amusement & Entertainment |
| Advocates for Homeless Families, Inc. | (301) 662-2003 | Non-Profit Organizations |
| Aerotek | (240) 629-7100 | Employment Services |
| AFLAC - Edwards | 301-685-6256 | Insurance Agencies/ Brokers |
| AFLAC - Fran Shaffer-Cofer | (301) 663-0560 | Insurance Agencies/ Brokers |
| AFLAC - Sandwick | 301-473-7057 | Insurance Agencies/ Brokers |
| AFLAC Independent Associate | 240-393-1397 | Insurance Agencies/ Brokers |
| Aircraft Owners & Pilots Association | (301) 695-2000 | Associations |
| Akonni Biosystems Inc. | (301) 698-0101 | Biomedical/ Biotechnology |
| Alcoa Eastalco Works | (301) 662-6100 | Manufactures/Processors |
| Aldi Inc. | (301) 360-9915 x113 | Grocery |
| Alexanders, LLC | 301-874-1831 | Restaurants/Cafes |
| Alicia L Sportswear | (301) 662-2722 | Retailers |
| All Around Plumbing, Inc. | (301) 829-6745 | Plumbing Services/Supplies |
| Alliance for Affordable Services | 301-293-2456 | Health Insurance |
| Allied Waste | (301) 694-6495 | Waste Management |
| Allstate Insurance/Rojewski/Holz Ins. Svs, LLC | (301) 620-0604 | Insurance Agencies/ Brokers |
| Allstate Insurance-Musser | 301-898-2851 | Insurance Agencies/ Brokers |
| Alzheimer's Association, Greater MD Chapter | (301) 696-0315 | Health Services/Doctors Offices |
| Amber Hill Physical Therapy, Inc. | (301) 663-1157 | Physical Therapy |
| American Cancer Society | (301) 733-8272 | Non-Profit Organizations |
| American Diabetes Association | (410) 265-0075 x4675 | Non-Profit Organizations |
| American Disposal Systems Inc. | (301) 695-0080 | Waste Management |
| American Health Assistance Foundation | 301-948-3244 | Non-Profit Organizations |
| American Office | (240) 520-3301 | Office Furniture |
| American Radiology Services | 443-465-5217 | Medical |
| American Red Cross Frederick County Chapter | (301) 662-5131 | Non-Profit Organizations |
| An Amethyst Awakening | 301-682-4789 | |
| The Arc of Frederick County | (301) 663-0909 | Non-Profit Organizations |
| Aspire Women's Clothing Boutique, LLC | (301) 695-9690 | Clothing |
| Asuncion Dental Group | (301) 620-8882 | Dentists |
| ATD Solar & Security, Inc. | (301) 607-4406 | Windows & Window Treatments |
| Audio-Video Group | (301) 668-4448 | Audio/Video Production |
| Ausherman Development Corporation | (301) 620-4444 | Developers |
| Auto Trim Design | (301) 662-7443 | Automotive |
| Ayaya Communication & Installers | 240-586-0770 | |