| Name | Phone | Category |
| Cafe 611 | (301) 631-1460 | Restaurants/Cafes |
| Cakes for Cause | (240) 344-0295 | Non-Profit Organizations |
| Camden Clearbrook | (301) 682-4766 | Apartments |
| Canapes, Incorporated | (301) 663-8220 | Caterers |
| Cancer Care Center of Frederick | 301-695-6777 | Medical |
| Cancer Care Center of Frederick - Mt. Airy | 301-698-6777 | Physicians / Surgeons |
| Cangene Plasma Resources Frederick | 301-696-8110 | Blood Banks & Centers |
| Cannon Hill Logistics | (301) 631-2984 | Fulfillment Services |
| Career Firefighters Association of Frederick County | (301) 573-0740 | Non-Profit Organizations |
| Carmack Insurance Group, Inc. | (301) 662-4119 | Insurance Agencies/ Brokers |
| Carpel Video, Inc. | 301-694-3500 | Digital Copying |
| Carriage House Inn | (301) 447-2366 | Restaurants/Cafes |
| Carroll Valley Resort | 717-642-8211 | Golf/Country Clubs & Shops |
| Catoctin Mountain Park | (301) 663-6571 | Parks |
| Catoctin Popcorn Company | (301) 682-4000 | Food |
| Global Wildlife Trust, Inc. | (301) 271-4922 | Wildlife / Zoo |
| CBIZ Financial Solutions | (301) 784-2343 | Investment Management |
| Ceresville Mansion | (301) 694-5111 | Conference/Meeting Facilities |
| Cetrom Information Technology, Inc. | 240-631-8500 | Information Technology |
| Chairs & More Office Furniture, Inc | (301) 874-0422 | Office Furniture |
| Champion Billiards Sports Cafe | 301-846-0089 | Restaurants/Cafes |
| Chapin and Associates, LLC | (240) 436-6200 | Real Estate Companies |
| Checkmate | (301) 631-5234 | Payroll Services |
| Chesapeake Public Strategies | 301-570-4582 | Marketing/Promotion |
| Chevy Chase Bank | (301) 698-3031 | Banks/savings/loans |
| Chevy Chase Bank - New Design Rd. | (301) 663-7840 | Banks/savings/loans |
| Children's Center Group, Inc. | (410) 489-5458 | Childcare |
| CiCi's Pizza | 540-435-1206 | Restaurants/Cafes |
| Cintas Corporation | (301) 874-8352 | Embroidery |
| CitiMortgage, Inc. | (301) 696-4113 | Mortgage Services |
| Clagett Enterprises, Inc. | 301-663-6009 | Real Estate Companies |
| Clark Welding and Fabricating Company, Inc. | 301-694-6161 | Welding, Fabrication & Repair |
| Classic Landscaping | (301) 898-3700 | Lawn/Garden/Landscaping Care |
| Clay Oven | 301-631-2004 | Restaurants/Cafes |
| Cleaning Supreames | (240) 575-0105 | Cleaning/Janitorial |
| Clearview Car Care | (301) 631-0050 | Automotive Services |
| Clerk of the Circuit Court | (301) 600-1975 | Government Agencies |
| Clinical Research Management, Inc. | (301) 620-1987 | Biomedical/ Biotechnology |
| Clintel Services, Inc. | 301-916-6100 | |
| CLSI | (301) 662-1799 | Surveyors |
| CLSI - Westminster | (410) 848-1790 | Surveyors |
| CLYM Environmental Services, LLC | 301-694-6000 | Recycling Companies |
| CMW Group, Inc. | (301) 631-2995 | Architects |
| Coldwell Banker Innovations | 301-662-8600 | Real Estate Companies |
| Colonial Jewelers | (301) 663-9252 | Retailers |
| Comcast | (301) 625-3410 | Communications |
| Comcast Spotlight | (301) 668-3140 | Advertising |
| Comcast-Frederick, MD | (301) 662-6822 | Communications |
| Comfort Inn | (301) 668-7272 | Lodging/Hotels & Motels |
| Commissioners of Thurmont | (301) 271-7313 | Municipality |
| Community Living, Inc. | (301) 663-8811 | Non-Profit Organizations |
| Community Radiology Associates, Inc. | 301-607-0444 | Medical |
| Community Radiology Associates, Inc. | 301-438-5003 | Medical |
| Complete Document Solutions Maryland,LLC | (301) 825-9220 | Copier Sales & Service |
| ComSource, Inc. | 240-379-1702 | Telecommunications |
| COMSTAR Federal Credit Union | (301) 975-9811 | Credit Union |
| Conewago Enterprises, Inc. | (717) 632-7722 | Construction/ General Contractors |
| Conjostudios, LLC | (301) 606-7794 | Audio/Video Production |
| Connie Phillips Insurance Inc. | (301) 662-5717 | Insurance Agencies/ Brokers |
| Mike Conord | (301) 874-5630 | |
| Conquest Web Design & Hosting | (240) 215-3750 | Web Design |
| Corporate Exposure Advertising Specialties | (301) 663-0333 | Promotional Products |
| Corporate Occupational Health Solutions | (240) 566-3001 | Health Services/Doctors Offices |
| Corporate Office Properties Trust (COPT) | (443) 285-5400 | Developers |
| Cort Furniture Rentals | 443-597-3711 | Furniture |
| CORVUS Business Solutions, LLC | 240-405-9174 | Sales Training |
| Cosmetic and Skin Surgery Center | (301) 698-2424 | Dermatology |
| Costco Wholesale | (301) 644-1483 | Warehouse Club |
| Cost-Seg-Pro, LLC | 301-367-7713 | Non-Profit Organizations |
| CQI Associates LLC | 443-677-8870 | Energy Services |
| Creekside Plaza Office Suites & Conference Center | (301) 673-2400 | Conference/Meeting Facilities |
| Creekside Plaza, LLC | (301) 695-3020 | Property Management |
| Crestwood Village Homeowners Association Inc. | (301) 662-1138 | Associations |
| Cruise Holidays of Frederick | 301-631-1300 | Cruise/Travel Services |
| Cruise Planners | 301-696-1611 | Travel Agencies |
| Crystal Park Apartments | 301-662-8887 | Apartments |
| Custom Imprints | 301-694-0000 | Advertising |
| CWP Tech Solutions | (301) 662-6219 | Computers/Internet |
| CycleNet | (800) 567-0527 | Printers |