| Name | Phone | Category |
| A Bloom, Ltd. | 301-898-5550 | Retail |
| A Corner Office LLC | 301-696-5701 | Business and Commercial Services |
| A Dessert for Me | 240-457-2811 | Catering |
| A Tasty Nosh | 301-668-2408 | Restaurants, Cafes, Eateries |
| A.D.P. Inspections, Inc. | 301-580-6844 | Real Estate |
| AAA Car Care Insurance Travel Center | 240-397-7414 | Automotive Services and Dealerships |
| AAA Mid-Atlantic | 301-663-4161 | Nonprofit |
| AASHTO Materials Reference Laboratory/Cement & Concrete | 240-436-4800 | Engineering |
| Acacia Fusion Bistro | 301-694-3015 | Restaurants, Cafes, Eateries |
| ACE Mentoring Program of Frederick | 240-344-1510 | Education, Training, Coaching |
| Acela Technologies, Inc. | 301-846-9060 | IT, Software, Computer Services |
| Adcomm Digitel | 301-682-5333 | Telecommunications |
| ADTEK Engineers, Inc. | 301-662-4408 | Engineering |
| Advance - The Document Specialists | 410-252-4800 | Equipment and Supplies |
| Advanced Urgent Care of Frederick | 240-379-7776 | Doctors and Health Services |
| Adventure Park USA | 301-865-6800 | Entertainment, Recreation, and Attractions |
| Advocates for Homeless Families, Inc. | 301-662-2003 | Nonprofit |
| Aeroseal of Maryland | 301-663-9112 | Construction, Contracting, Building |
| Aerotek | 240-629-7100 | Employment, Staffing, Human Resources |
| AFAB Lab, LLC | 240-313-6044 | Biotechnology and Biomedical |
| Air Repair Heating & Cooling, LLC | 240-409-2636 | HVAC, Plumbing, and Electrical Contractors |
| Aircraft Owners & Pilots Association | 301-695-2000 | Association |
| Aire Serv of Frederick | 301-845-4848 | HVAC, Plumbing, and Electrical Contractors |
| Airport Xpress, Inc. | (301) 668-4000 | |
| Akonni Biosystems Inc. | 301-698-0101 | Biotechnology and Biomedical |
| Alcoa Eastalco Works | 301-696-1753 | Manufacturing, Processing, and Distribution |
| Alexanders Restaurant | 301-874-1831 | Restaurants, Cafes, Eateries |
| Alicia L Sportswear | 301-662-2722 | Retail |
| Alizee Pathology | 240-356-0056 | Biotechnology and Biomedical |
| All Around Plumbing, Inc. | 301- 829-6745 | Construction, Contracting, Building |
| All Saints' Episcopal Church | 301-663-5625 | Churches, Synagogues, and Faith Communities |
| Allagash Group, LLC | 410-740-8701 | Consulting |
| Allied Technologies and Consulting, LLC | 301-696-1030 | Research and Development |
| Allied Waste | 301-223-4629 | Waste Management and Recycling |
| Allstate Insurance - Cochrane Agency | 301-696-0555 | Financial and Investment Services |
| ALTEK Information Technology | 301-695-4440 | IT, Software, Computer Services |
| Alzheimer's Association, Greater MD Chapter | 301- 696-0315 | Doctors and Health Services |
| AM 1450 The Source | 301-637-6736 | Marketing, Advertising, and Communications |
| Amber Hill Phyiscal Therapy, Inc. - Urbana | 240-529-0175 | Doctors and Health 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 Laser Skincare | 301-662-6888 | Salons and Spas |
| American Lumper Services, LLC | 301-639-4929 | Manufacturing, Processing, and Distribution |
| American National Properties | 301-874-8640 | Real Estate |
| American Red Cross Frederick County Chapter | 301-662-5131 | Nonprofit |
| American Spine | 301-682-7246 | Doctors and Health Services |
| Amerigas | 301-620-9046 | HVAC, Plumbing, and Electrical Contractors |
| Ameritel Corporation | 301-662-5000 | Equipment and Supplies |
| Amethyst Technologies | 443-543-5576 | Engineering |
| Amy Benton. PR | 240-446-4309 | Consulting |
| An Evening on the Riviera | 301-663-9160 | Nonprofit |
| Anything in Stained Glass | 301-378-2218 | Retail |
| Anytime Fitness Frederick | 301-378-2906 | Education, Training, Coaching |
| Apex Home Loans | 240-268-3442 | Banks and Credit Unions |
| ArachnidWorks, Inc. | 240-285-9844 | Marketing, Advertising, and Communications |
| Aronson, LLC | 301-231-6200 | Accounting |
| 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 |
| AT&T | 301-682-5766 | Telecommunications |
| Audio Design Solutions, Inc. | 301-607-6607 | Business and Commercial Services |
| Audio-Video Group | 301- 668-4448 | Photography and Videography |
| Ausherman Family Foundation | 301-620-4443 | Nonprofit |
| Ausherman Properties | 301-620-4444 | Real Estate |
| Auto Trim Design | 301-662-7443 | Automotive Services and Dealerships |
| Automatic Data Processing (ADP) | 484-707-0228 | Business and Commercial Services |
| Avanti Marble & Granite | 301-874-3900 | Retail |