| Company | Rockville Employee Count |
| U.S. Food and Drug Administration | 9300 |
| Montgomery County Government | 2101 |
| Westat, Inc | 1900 |
| Montgomery County Board of Education | 1876 |
| Montgomery College | 1427 |
| Human Genome Sciences | 900 |
| Kaiser Permanente | 900 |
| Community Services for Autistic Adults and Children | 600 |
| City of Rockville | 520 |
| Booz Allen Hamilton | 500 |
| Lockheed Martin Information Systems | 500 |
| Mann Bracken, LLC (Formerly Known As Wolpoff & Abramson, LLP) | 500 |
| US Pharmacopeia | 470 |
| BioReliance Corporation | 447 |
| EU Services | 378 |
| Banner Life Insurance Company | 370 |
| Grunley Construction Co. Inc. | 350 |
| Legal & General America/Banner Life Insurance | 350 |
| Giant Food | 326 |
| J. Craig Venter Institute | 326 |
| Agency for Healthcare Research and Quality | 325 |
| IQ Solutions | 306 |
| Adventist Healthcare | 302 |
| BAE Systems, Inc. | 300 |
| Client Network Services, Inc. (CNSI) | 300 |
| Comcast | 300 |
| NCR Corporation | 300 |
| TheraCom | 300 |
| Emmes Corporation | 294 |
| James G. Davis Construction Corporation | 285 |
| Adecco | 250 |
| American Speech-Language-Hearing Association (ASHA) | 250 |
| Collingswood Nursing Facility | 250 |
| Fisher BioServices | 250 |
| Risk Metrics Group | 250 |
| UMBI - University of Maryland Biotechnology Institute | 250 |
| Woodmont Country Club | 250 |
| Aronson & Company | 240 |
| Henry M. Jackson Foundation | 234 |
| I.M. Systems Group | 225 |
| Thomson Reuters | 225 |
| UnitedHealthcare (Formerly Known As Mamsi) | 204 |
| Automatic Data Processing (ADP) | 200 |
| Bioscience International | 200 |
| Clear Channel Communications | 200 |
| Computer Sciences Corporation (CSC) | 200 |
| Forrester Construction Co. | 200 |
| Otsuka American Pharmaceutical, Inc. | 200 |
| Shulman, Rogers, Gandal, Pordy & Ecker | 200 |
| JDA Software Group, Inc. | 198 |
| Avendra | 195 |
| EDS | 180 |
| HealthExtras, Inc./Catalyst Health Solutions | 180 |
| Whole Foods Markets, Inc. | 180 |
| Bioqual | 175 |
| Jewish Social Services Agency | 160 |
| Shady Grove Fertility Center | 160 |
| Smith Litho | 160 |
| Spirent Communications | 156 |
| Emcor Services, Combustioneer Corporation | 155 |
| Creative Computing Solutions Inc | 153 |
| MDA Federal | 150 |
| Northrop Grumman Infotech | 150 |
| PSI International, Inc. | 150 |
| The Biostatistics Center | 150 |
| Montgomery Hospice Society | 145 |
| EMC CORP | 143 |
| Aeras Global TB Vaccine Foundation | 140 |
| MCT Federal Credit Union | 140 |
| Rockville Nursing Home, Inc. | 140 |
| MacroGenics, Inc. | 135 |
| Computer Packages, Inc. | 130 |
| Vanguard Realty Group | 130 |
| SRA International | 128 |
| Hilton Washington DC/Rockville Executive Meeting Center | 126 |
| Capital Technology Information Services (CTIS) | 125 |
| Catalyst Health Solutions Inc. | 125 |
| Federal Realty Investment Trust | 125 |
| InvestorPlace Media LLC / Phillips Investment Resources | 125 |
| AARP | 120 |
| Gordon Biersch | 120 |
| Institute for Bioscience and Biotechnology Research (IBBR), formerly Center for Advanced Research in Biotechnology (CARB) | 120 |
| Telvent Farradyne | 120 |
| Lexus | 116 |
| Intelligent Automation, Inc. | 115 |
| Pel-Bern Electric | 115 |
| Rockville Fuel and Feed Company, Inc. | 112 |
| Access Intelligence | 110 |
| Stein, Sperling, Bennett, De Jong, Driscoll & Greenfeig, P.C. | 104 |
| Congressional Motors | 101 |
| AETEA Information Technology, Inc. | 100 |
| DST Health Solutions(used to be Amysis) | 100 |
| Greystone Grill | 100 |
| InfoZen | 100 |
| Metropolitan Regional Informatin Systems, Inc. (MRIS) | 100 |
| Micro Focus International | 100 |
| Midwest Research Institute - National Capital Regional Laboratory | 100 |
| NIH Federal Credit Union | 100 |
| Quest Software | 100 |
| The Legacy | 100 |
| Z-Tech, An ICF International Company (Formerly Known As Z-Tech Corporation) | 100 |