| Cromlech Invest AS | Professional & scientific | 2014 |
| Crystal AS | Other services | 2017 |
| CS Consult AS | Professional & scientific | 2025 |
| CSJ & Co Eiendom AS | Real estate | 2007 |
| CSJ Busterudkleiva 1 AS | Real estate | 2007 |
| CSJ Eiendom AS | Real estate | 2007 |
| CSJ Hougens Gate 1 AS | Real estate | 2009 |
| CSJ Kristian Augusts Gate 4 AS | Real estate | 2008 |
| Ctek Norway AS | Wholesale & retail | 2021 |
| CUBE8 AS | Professional & scientific | 2018 |
| CUBE8 Gallery AS | Real estate | 2018 |
| Custardlabs AS | Information & communication | 2014 |
| Cvlia AS | Information & communication | 2026 |
| Cæsar AS | Real estate | 2012 |
| D&D Consult AS | Wholesale & retail | 2007 |
| D-Hus & Blikk AS | Construction | 2019 |
| D.E.T AS | Professional & scientific | 1993 |
| Dabv AS | Professional & scientific | 2020 |
| Dag Prosjekt AS | Construction | 1996 |
| Dagligvare Lislebyveien AS | Wholesale & retail | 2024 |
| Dagsander Invest AS | Real estate | 2002 |
| Dahl Trafikkskole AS | Education | 2017 |
| Dahles Auto Fredrikstad AS | Other services | 1991 |
| Dahles Auto Råbekken AS | Wholesale & retail | 1989 |
| Dahlmag AS | | 2025 |
| Dakota AS | Professional & scientific | 2012 |
| Dammyr Bygg AS | Construction | 2007 |
| Dampskibsbryggen Eiendom AS | Real estate | 2000 |
| Dampskipsbrygga 10 AS | Real estate | 2004 |
| Dampskipsbryggen 8 AS | Real estate | 2005 |
| Danilift Norge AS | Wholesale & retail | 1985 |
| Danos AS | Hospitality | 2001 |
| Dardeau Holding AS | Financial services | 2018 |
| Dark Fredrikstad AS | Professional & scientific | 2015 |
| Databasesentralen AS | Information & communication | 2012 |
| Dawgleg AS | Wholesale & retail | 2026 |
| DB Prosjekt AS | Professional & scientific | 2021 |
| DBJ Invest AS | Financial services | 2005 |
| De Lange Invest | | 2024 |
| Deg & Co. AS | Professional & scientific | 2012 |
| Dehn Design AS | Professional & scientific | 2012 |
| Delages AS | Information & communication | 2026 |
| Delonic Technology Group AS | Information & communication | 2002 |
| Delta Energy Solutions AS | | 2021 |
| Delta Transport AS | Transport & logistics | 2022 |
| Deluxe Frisør AS | Other services | 2023 |
| Deluxe Spa Clinic AS | Other services | 2012 |
| Denim Destination Fredrikstad AS | Wholesale & retail | 2025 |
| Dentacare AS | Wholesale & retail | 2005 |
| Dente Holding AS | Health & social care | 2020 |
| Dentzone AS | Health & social care | 2003 |
| Depart AS | Administrative & support | 2026 |
| Deroma Brygga AS | Hospitality | 2021 |
| Designik Holding AS | | 2024 |
| Desp.No Da | Information & communication | 2004 |
| Destination Holding AS | Financial services | 2015 |
| Dikeveien 45 Eiendom AS | Real estate | 2018 |
| Dikeveien 48 Eiendom AS | Real estate | 2006 |
| Dikeveien 55 Eiendom AS | Real estate | 2020 |
| Dikeveien Eiendom AS | Real estate | 2005 |
| Dikeveien Nord Eiendom AS | Real estate | 2006 |
| Dimco AS | Professional & scientific | 2011 |
| Din Kjøkkenhage AS | Wholesale & retail | 2021 |
| Din Veileder AS | Health & social care | 2018 |
| Diofant AS | Professional & scientific | 2021 |
| Dis Design AS | Wholesale & retail | 2015 |
| Distribusjonsservice AS | Transport & logistics | 1990 |
| Ditt Behov Ans | | 1991 |
| Divan Fredrikstad AS | Hospitality | 2016 |
| DK Takst Og Bygg AS | Real estate | 2024 |
| DK. Holding AS | Real estate | 2010 |
| Doktor Sypula AS | Health & social care | 2005 |
| Domino Interiør AS | Wholesale & retail | 2006 |
| DP Fredrikstad AS | Hospitality | 2020 |
| Dracon AS | Professional & scientific | 1994 |
| Dragen Pub AS | Hospitality | 2016 |
| Drammensveien 39 Hjemmel AS | Real estate | 2014 |
| Drivhuset AS | | 2025 |
| Druekompaniet AS | Professional & scientific | 2020 |
| Drywood OY AB | Wholesale & retail | 1997 |
| DTZ Eiendom AS | Real estate | 2026 |
| Duhok-Frisør AS | Other services | 2022 |
| Dunder Bistro AS | Hospitality | 2025 |
| Dvi Tannklinikk AS | Health & social care | 2018 |
| Dyar Holding AS | Information & communication | 2013 |
| DZT AS | | 2025 |
| Dør & Vindu Fredrikstad AS | Wholesale & retail | 2007 |
| Dør Og Vindu AS | Wholesale & retail | 2002 |
| E&E Holding AS | Professional & scientific | 2024 |
| E. Larsen Holding AS | Real estate | 2015 |
| Easycorp AS | Information & communication | 2024 |
| Eat Thai Holding AS | Hospitality | 2020 |
| Eb Gass Fredrikstad AS | Wholesale & retail | 2022 |
| Ebm Bygg AS | Construction | 2023 |
| Eborg AS | Professional & scientific | 2012 |
| Eco Finans Fredrikstad AS | Professional & scientific | 2019 |
| Ecobinio AS | Information & communication | 2023 |
| Eddy's Montasje AS | Construction | 2012 |
| Edesberg Holding AS | | 2021 |
| Edi Transport AS | Transport & logistics | 2024 |