| Name | Phone | Category |
| A Corner Office LLC | 301-696-5701 | Business and Commercial Services |
| A Cut Above Catering | 301-663-1516 | Catering |
| AAA Car Care Insurance Travel Center | 240-397-7414 | Automotive Services and Dealerships |
| AAA Mid-Atlantic | 301-663-4161 | Nonprofit |
| AARP Maryland | 410-895-7602 | Nonprofit |
| Ability Prosthetics & Orthotics, Inc. | 717-337-2273 | Doctors and Health Services |
| Able & Willing International Education Foundation, Inc. | 301-685-3282 | Schools and Colleges |
| Abloom, Ltd. | 301-898-5550 | Retail |
| Acacia Fusion Bistro | 301-694-3015 | Restaurants, Cafes, Eateries |
| ACDC, Inc. | 301-418-6070 | IT, Software, Computer Services |
| ACE Mentoring Program of Frederick | 240-344-1510 | Education, Training, Coaching |
| Acela Technologies, Inc. | 301-846-9060 | IT, Software, Computer Services |
| Adams County Winery | 717-334-4631 | Wineries, Breweries, and Liquor Stores |
| Advance - The Document Specialists | 410-252-4800 | Equipment and Supplies |
| Advanced Urgent Care of Frederick | 240-379-7776 | Doctors and Health Services |
| Adventist Health Care-Germantown | 301-315-3042 | Doctors and Health Services |
| Adventure Park USA | 301-865-6800 | Entertainment, Recreation, and Attractions |
| Advocates for Homeless Families, Inc. | 301-662-2003 | Nonprofit |
| Aerotek | 240-629-7100 | Employment, Staffing, Human Resources |
| AFLAC - Eyler/Rippeon | 410-596-5792 | Insurance Agents and Brokers |
| AFLAC, Frederick | 301-418-6018 | Insurance Agents and Brokers |
| Aircraft Owners & Pilots Association | 301-695-2000 | Association |
| Airgas | 301-663-0644 | Construction, Contracting, Building |
| Akonni Biosystems Inc. | 301-698-0101 | Biotechnology and Biomedical |
| Alcoa Eastalco Works | 301-662-6100 | Manufacturing, Processing, and Distribution |
| Alexanders Restaurant | 301-874-1831 | Restaurants, Cafes, Eateries |
| Alicia L Sportswear | 301-662-2722 | Retail |
| Alizee Pathology | 240-422-0666 | Biotechnology and Biomedical |
| All Around Plumbing, Inc. | 301- 829-6745 | Construction, Contracting, Building |
| All in a Dayz Work | 301-676-8018 | Business and Commercial Services |
| All Saints' Episcopal Church | 301-663-5625 | Churches, Synagogues, and Faith Communities |
| All Walks of Life Pet Services | 717-339-9955 | Veterinary Services and Pet Care |
| Allegra Printing | 301-662-1102 | Printing, Engraving, Promotional Products |
| Allied Property Maintenance Group/Allied Construction Group | 240-586-2191 | Property Management and Maintenance |
| Allied Technologies and Consulting, LLC | 301-696-1030 | Research and Development |
| Allied Waste | 301- 694-6495 | Waste Management and Recycling |
| Allstate Insurance - Cochrane Agency | 301-696-0555 | Financial and Investment Services |
| Allstate Insurance - Mountain Valley Insurance Services, LLC | 301-620-0604 | Insurance Agents and Brokers |
| ALTEK Information Technology | 301-695-4440 | IT, Software, Computer Services |
| Alzheimer's Association, Greater MD Chapter | 301- 696-0315 | Doctors and Health Services |
| Amadeo & Gaines, LLC | 301-418-6393 | Business and Commercial Services |
| Amber Hill Physical Therapy, Inc. | 301-663-1157 | Doctors and Health Services |
| American Association for Laboratory Accreditation (A2LA) | 301-644-3248 | Nonprofit |
| American Cancer Society | 301-733-8272 | Nonprofit |
| American Diabetes Association | 410- 265-0075 | Nonprofit |
| American Disposal Systems Inc. | 301-695-0080 | Waste Management and Recycling |
| American Health Assistance Foundation | 301-948-3244 | Nonprofit |
| American Radiology Services | 443-465-5217 | Doctors and Health Services |
| American Red Cross Frederick County Chapter | 301-662-5131 | Nonprofit |
| American Spine Center | 301-682-7246 | Doctors and Health Services |
| Amethyst Technologies | 443-543-5576 | Engineering |
| Ananda Shala Yoga & Pilates Studio | 301-682-9642 | Salons and Spas |
| Angelcakes, LLC | 301-898-2666 | Retail |
| Antietam Travel Service, Inc | 301-662-8080 | Travel, Tourism, and Transportation |
| Anything in Stained Glass | 301-378-2218 | Retail |
| Anytime Fitness Frederick | 301-378-2906 | Education, Training, Coaching |
| The Arc of Frederick County | 301-663-0909 | Nonprofit |
| Archive Design Services, Inc. | 301-620-2090 | Architecture and Design |
| Artifex Contractors | 301-695-0557 | Construction, Contracting, Building |
| Aspire Women's Clothing Boutique, LLC | 301-695-9690 | Retail |
| Asuncion Dental Group | 301-620-8882 | Doctors and Health Services |
| ATD Solar & Security, Inc. | 301-607-4406 | Construction, Contracting, Building |
| Audio-Video Group | 301- 668-4448 | Photography and Videography |
| Ausherman Development Corporation | 301-620-4444 | Commercial and Residential Development |
| Ausherman Family Foundation | 301-620-4443 | Nonprofit |
| Auto Trim Design | 301-662-7443 | Automotive Services and Dealerships |