| Høgrika AS | Real estate | 2025 |
| I.T.O. Holding AS | | 2024 |
| Idrettsveien 9 AS | Real estate | 1999 |
| Incloud AS | Wholesale & retail | 2017 |
| Indre Østfold Nærradio SA | Information & communication | 1998 |
| Jakt & Villmark AS | Wholesale & retail | 2020 |
| Jeb Eiendom AS | Real estate | 1988 |
| Jens KR Mjørud AS | Real estate | 1991 |
| JH Mekaniske AS | Manufacturing | 2016 |
| Jim Consult AS | Professional & scientific | 2004 |
| Jim Eiendom AS | Professional & scientific | 1998 |
| Jost Norge AS | Wholesale & retail | 1985 |
| JP Næristorp Invest AS | | 2018 |
| JR Eiendom AS | Real estate | 2018 |
| K. Stalsberg Holding AS | | 2025 |
| Kaaen Rakkestad Elektro AS | Construction | 2004 |
| Kaaterud Holding AS | | 2024 |
| Kaiae Holding AS | | 2023 |
| Kaiae Invest AS | | 2023 |
| Kalkmaling Norge AS | Wholesale & retail | 2023 |
| Kame Invest AS | Real estate | 2016 |
| Kamled AS | Wholesale & retail | 2011 |
| Karlson Transport AS | Transport & logistics | 2006 |
| Kaso Invest AS | Real estate | 2014 |
| KB1 Gruppen AS | | 2020 |
| Kenneth Veiby Holding AS | | 2015 |
| Kildeveien AS | Real estate | 2018 |
| Kirkeng Bil AS | Other services | 1999 |
| KJ Montasje AS | Construction | 2021 |
| KJ Montasje Eiendom AS | Real estate | 2025 |
| Kjelda AS | Real estate | 1973 |
| KK Gravdal AS | | 2022 |
| KL Harlem AS | | 2025 |
| Kloberget Invest AS | Professional & scientific | 2005 |
| Klypa Bil AS | Other services | 2019 |
| Knirkefri AS | Health & social care | 2020 |
| Knivsø Marine AS | Real estate | 2007 |
| Knivsøveien Eiendom AS | Real estate | 2019 |
| Knut Robert Finnestad AS | Real estate | 2016 |
| Ko Harlem AS | | 2025 |
| KODE15 AS | Professional & scientific | 2006 |
| Kolstad Eierskap AS | | 2019 |
| Koltek AS | Manufacturing | 2015 |
| Kopperud Murtnes Bygg AS | Construction | 1992 |
| Kopperud Murtnes Eiendom AS | Real estate | 1998 |
| Korndrift SA | Administrative & support | 2003 |
| Kraugerud AS | Real estate | 2020 |
| Kraugerud Invest AS | Real estate | 2024 |
| Kraugerudåsen AS | Real estate | 2025 |
| Kriscorn Invest AS | Financial services | 2017 |
| L&P Eiendom AS | Real estate | 2021 |
| Lagerveien 3 AS | Construction | 2022 |
| Lagerveien AS | Real estate | 2026 |
| Lan Holding AS | Financial services | 2007 |
| Landbrukstjenester Østfold SA | Agriculture & fishing | 1995 |
| Langsholt Glass Service Da | Construction | 2009 |
| Lansel AS | | 2020 |
| Larsen Eiendomsservice AS | Real estate | 2005 |
| Larsen Kolstad Bygg AS | Construction | 2019 |
| Larsen Renhold AS | Administrative & support | 2014 |
| LBH Nordic Compensators AS | Wholesale & retail | 2015 |
| Leia Radio AS | Wholesale & retail | 2022 |
| Leif André Haugom AS | Construction | 2012 |
| LF Harlem AS | | 2025 |
| Lien Elektro AS | Construction | 2014 |
| Lill's Dyreverden AS | Wholesale & retail | 2026 |
| Lin-Tin Eiendom AS | Real estate | 2014 |
| Lin-Tin Holding AS | Real estate | 1997 |
| Lindemark Transport AS | Transport & logistics | 2005 |
| Linhk AS | Financial services | 2016 |
| Lise's Hundeskole AS | Education | 2020 |
| Logopedhuset AS | Health & social care | 2025 |
| Loren Renhold AS | Administrative & support | 2022 |
| Lunsjbar'N AS | Hospitality | 2023 |
| Lysaker Blikk Og Ventilasjon AS | Construction | 2014 |
| M&M Frisør AS | Other services | 2013 |
| M-Lundeby Invest AS | Real estate | 2020 |
| M.Syversen Holding AS | Real estate | 2020 |
| Maborg AS | Real estate | 2020 |
| Mad Viking Barbershop AS | Other services | 2019 |
| Magoo AS | Wholesale & retail | 2015 |
| Malina Invest AS | Real estate | 2017 |
| Marthe Røsnæs AS | | 2021 |
| Maskinentreprenør R. Tobiassen AS | Construction | 2025 |
| Mathuset Winther AS | Hospitality | 2019 |
| Mccm Invest AS | Financial services | 2022 |
| MCH Holding AS | | 2019 |
| Mcol AS | Education | 2022 |
| Mecsupport AS | Manufacturing | 2019 |
| Melby Maskinstasjon AS | Wholesale & retail | 2005 |
| Messaconsult AS | Professional & scientific | 2020 |
| Methliewebdesign AS | Information & communication | 2025 |
| MG Tømrermester AS | Construction | 2024 |
| Midtfjell Holding AS | | 2024 |
| Mjørud AS | Manufacturing | 1998 |
| Mjørud Gruppen AS | Manufacturing | 1987 |
| Mjørud Industribygg AS | Real estate | 2011 |
| Mjørudgata Utvikling AS | Real estate | 2024 |
| ML Holding. AS | | 2025 |
| Morten Fixit AS | Construction | 2016 |