| Comex Scientific LLC | San Diego | CA | Subcontractor |
| Commissioning Consultants, LLP | Greer | SC | Subcontractor |
| Commissioning Team LLC | Arlington Heights | IL | Subcontractor |
| Commlargo Inc. | Salem | MO | Subcontractor |
| Commnet, LLC | Forest Hill | MD | Subcontractor |
| Commtech Systems Inc. | El Cajon | CA | Subcontractor |
| Communications Development Company (CDC) | Amman | | Subcontractor |
| Compania De Consultanta In Energie Si Mediu Sa | Bucharest | | Subcontractor |
| Compass Commissioning & Design, LLC | Hixson | TN | $0 |
| Complete Automation Controls, LLC | Swedesboro | NJ | Subcontractor |
| Complete Networks Inc. | North Ridgeville | OH | Subcontractor |
| Compliance Services Group, Inc. | Lubbock | TX | $0 |
| Composito LLC | New York | NY | Subcontractor |
| Computational Hydraulics Inc. | Guelph | ON | $0 |
| Comspec Engineering, Inc. | Honolulu | HI | Subcontractor |
| Conarch LLC | Nokesville | VA | Subcontractor |
| Concord Engineering Group, Inc. | Voorhees | NJ | $0 |
| Concorr Inc. | Sterling | VA | $0 |
| Condition Analyzing Corporation | Saint Johns | FL | $0 |
| Confluence Engineering Group, LLC | Seattle | WA | Subcontractor |
| Connect Engineering, D.P.C. | New York | NY | Subcontractor |
| Connecticut Reserve Technologies Inc. | Gates Mills | OH | Subcontractor |
| Consolidated Consultants Engineering Environment | Abu Dhabi | | Subcontractor |
| Consor North America, Inc. | Miami | FL | Subcontractor |
| Constantine Engineering Inc. | Fort Walton Beach | FL | Subcontractor |
| Construction-cad Solutions, Incorporated | Burr Ridge | IL | $0 |
| Construction Engineering Solutions, LLC | Fruita | CO | $0 |
| Construction Fabrication Services Inc. | Mobile | AL | Subcontractor |
| Construction Materials Engineers Inc. | Reno | NV | Subcontractor |
| Consul - Tech Engineering, PSC | San Juan | PR | Subcontractor |
| Continuum Engineering Inc. | Los Angeles | CA | $0 |
| Continuum Infrastructure Solutions, Inc. | Youngsville | NC | Subcontractor |
| Contrast, Inc. | Albuquerque | NM | $0 |
| Control Engineers, P.a. | Boise | ID | Subcontractor |
| Control System Solutions LLC | Tulsa | OK | Subcontractor |
| Control Technology, Inc. | Redmond | WA | Subcontractor |
| Cook, Flatt & Strobel, Engineers, P.a. | Topeka | KS | $0 |
| Copia LLC | Goshen | NH | $0 |
| Copilot Net, LLC | Frisco | TX | $0 |
| Core Engineers Consulting Group, Inc. | Washington | DC | $0 |
| Core Two Technology LLC | Sterling | VA | Subcontractor |
| Cornerstone Software Solutions Inc. | Orlando | FL | Subcontractor |
| Corporate Environmental Risk Management, L.L.C. | Atlanta | GA | Subcontractor |
| Corrosion Works, LLC | Colorado Springs | CO | Subcontractor |
| Corsair Technical Services LLC | Kirkland | WA | Subcontractor |
| Corscience GMBH & Co. Kg | Erlangen | | Subcontractor |
| Costech, Inc. | Winter Springs | FL | $0 |
| Counsilman Hunsaker & Associates, Inc. | Saint Louis | MO | Subcontractor |
| Covell Solutions Incorporated | Vienna | VA | Subcontractor |
| Coventry Associates, Inc. | West Boylston | MA | $0 |
| Covisus Corporation | Monrovia | CA | Subcontractor |
| Cowboy Programming Resources, Inc. | El Paso | TX | Subcontractor |
| Cowi North America, Inc. | Oakland | CA | Subcontractor |
| Cowles Consulting, LLC | Tolland | CT | Subcontractor |
| CPS Ltd. | Grand Forks | ND | Subcontractor |
| CQC Testing And Engineering, L.L.C | El Paso | TX | Subcontractor |
| Cr Access Consulting, LLC | Virginia Beach | VA | Subcontractor |
| Craft Designs Inc. | Huntsville | AL | Subcontractor |
| Crafton Tull & Associates, Inc. | Rogers | AR | $0 |
| Craftwater Engineering, Inc. | San Diego | CA | Subcontractor |
| Craig A. Smith & Associates, LLC | Riviera Beach | FL | Subcontractor |
| Craige Research, Inc. | Roslyn Heights | NY | $0 |
| Created Solutions Inc. | Harvest | AL | Subcontractor |
| Creative Aero Engineering Solutions Inc. | Long Beach | CA | $0 |
| Creative Engineering, L.L.C. | Bronxville | NY | Subcontractor |
| Creative Engineers, Inc. | New Freedom | PA | $0 |
| Creative Wx Solutions LLC | Mills River | NC | Subcontractor |
| Crenshaw Consulting Engineers, Inc. | Raleigh | NC | Subcontractor |
| Creve Coeur Research And Engineering Company, Inc. | Saint Louis | MO | Subcontractor |
| Crist Engineers, Inc. | Little Rock | AR | $0 |
| Critical Realm Corporation | San Jose | CA | Subcontractor |
| Crockett Engineering Consultants LLC | Columbia | MO | $0 |
| Crosslink Partners LLC | Colorado Springs | CO | Subcontractor |
| Cross-spectrum Acoustics, Inc. | East Longmeadow | MA | $0 |
| Csa, Inc. | Little Compton | RI | $0 |
| Cs Consulting Engineers, Inc. | Rockville | MD | Subcontractor |
| Cs Davidson Inc. | York | PA | $0 |
| C S Engineering, Inc. | Knoxville | TN | $0 |
| C & S Engineers Inc. | Syracuse | NY | Subcontractor |
| Csi Engineering Inc. | Laurel | MD | $0 |
| Csngineering LLC | Sarasota | FL | $0 |
| Csra Systems & Solutions LLC | Alexandria | VA | $0 |
| CSRS LLC | Baton Rouge | LA | $0 |
| CTL Engineering, Inc. | Columbus | OH | Subcontractor |
| Ctl/thompson, Inc. | Denver | CO | Subcontractor |
| Cubeworks Inc. | Ann Arbor | MI | Subcontractor |
| Cuc Consulting Corp. | Nokesville | VA | Subcontractor |
| Cundiff Engineering Inc. | Beaverton | OR | $0 |
| Cunningham Engineering, P.C. | Cookeville | TN | $0 |
| Curios Technologies LLC | San Diego | CA | Subcontractor |
| Curran-mcleod, Inc. | Portland | OR | $0 |
| Curry-wille And Associates Consulting Engineers, P.C., | Ames | IA | Subcontractor |
| Curtain Wall Design And Consulting, Incorporated | Dallas | TX | Subcontractor |
| Custom Analytical Engineering Systems, Inc. | Flintstone | MD | Subcontractor |
| Custom Engineering, Inc. | Independence | MO | Subcontractor |
| Custom Engineering Solutions, Inc. | Alpharetta | GA | Subcontractor |
| Custom Lab Software Systems, Inc. | Centerbrook | CT | Subcontractor |
| Custom Silicon Solutions, Inc. | Irvine | CA | Subcontractor |
| Custom Systems Integration Inc. | Binghamton | NY | Subcontractor |
| Custom Technologies, LLC | Millersville | MD | Subcontractor |
