| Horten Male Experten AS | Construction | 2024 |
| Horten Male Service AS | Construction | 2022 |
| Horten Mikrobryggeri AS | Manufacturing | 2015 |
| Horten Montessoriskole SA | Education | 2005 |
| Horten Revisjon AS | | 2025 |
| Horten Ridesenter AS | Arts & recreation | 2023 |
| Horten Rideskole AS | Arts & recreation | 2023 |
| Horten Rørleggerbedrift AS | Construction | 1983 |
| Horten Skipsreparasjoner AS | Manufacturing | 1988 |
| Horten Specsavers AS | Wholesale & retail | 2007 |
| Horten Stillasutleie AS | Administrative & support | 2020 |
| Horten Sushi Linden Park Takea AS | Hospitality | 2022 |
| Horten Søm & Salmakerverksted AS | Manufacturing | 2015 |
| Horten Ur Og Gull AS | Wholesale & retail | 2015 |
| Horten Ventilasjon Service AS | Construction | 2026 |
| Horten VVS AS | Construction | 2014 |
| Hortens Brygge Holding AS | Administrative & support | 2012 |
| Hortonn AS | Real estate | 2004 |
| HS Tech AS | Wholesale & retail | 2017 |
| Hsbs Group AS | Professional & scientific | 2015 |
| HTS Holding AS | Real estate | 2005 |
| Hug Holding AS | Wholesale & retail | 2017 |
| Huse Invest AS | Education | 2022 |
| Hvit Natt AS | Wholesale & retail | 2025 |
| Hvu Bygg AS | Construction | 2019 |
| Hvu Eiendom AS | Real estate | 2022 |
| Hylgert AS | | 2019 |
| Henriksen Eiendoms A/S | Real estate | 1987 |
| Håheim Eiendom AS | Real estate | 2025 |
| Håheim Invest AS | | 2025 |
| Håheim Kran Og Transport AS | Transport & logistics | 2025 |
| Håvi Holding AS | | 2020 |
| Høyden Vannverk SA | Water & waste | 1968 |
| I-Mente AS | Information & communication | 2013 |
| Idess Norway AS | Information & communication | 1992 |
| Idl AS | Information & communication | 2022 |
| Idr Huset AS | Real estate | 1987 |
| Iforkant AS | Professional & scientific | 2023 |
| Ignis Tjenester AS | Professional & scientific | 2024 |
| Ihlhaug Holding AS | Health & social care | 2023 |
| Ilda Care AS | Manufacturing | 2019 |
| Ilda Design, Jewelry by Camilla AS | Manufacturing | 2013 |
| Imingen Horten AS | Real estate | 2018 |
| Immensum AS | Real estate | 2013 |
| Indigo Dame Og Herrefrisør AS | Other services | 2015 |
| Indre Havneby AS | Real estate | 2012 |
| Indus Infotel AS | Information & communication | 2001 |
| Infrageo AS | Professional & scientific | 2022 |
| Innkjøpskontoret AS | Professional & scientific | 2013 |
| Inotek Survey AS | Professional & scientific | 2023 |
| Inpartner AS | Professional & scientific | 1995 |
| Inspira Interiørkontor AS | Professional & scientific | 2020 |
| Integrasjonssystemer AS | Information & communication | 1997 |
| Intervest AS | Real estate | 1986 |
| Intervest Miljø AS | Manufacturing | 2024 |
| Invicto AS | Wholesale & retail | 2010 |
| IT Consulting AS | Information & communication | 2000 |
| It-Systemer AS | Information & communication | 2004 |
| Its Pro AS | Real estate | 2010 |
| J. C. Broch AS | Manufacturing | 2018 |
| Jac. Jacobsen Da | Real estate | 2007 |
| Jacobsen & Sønn AS | Real estate | 2007 |
| Jat Holding AS | Real estate | 2019 |
| JBC Services AS | Professional & scientific | 2007 |
| JC Gaard AS | | 2023 |
| Jentene På Kaffe AS | Wholesale & retail | 2002 |
| Jernringen AS | | 2019 |
| JHN AS | Administrative & support | 2012 |
| Ji&B Holding AS | Construction | 2023 |
| JK Interiør AS | Wholesale & retail | 2021 |
| JL Staff Holding AS | | 2022 |
| JMC AS | Professional & scientific | 2000 |
| JMC Virksomhet AS | Hospitality | 2023 |
| Joba Invest AS | | 2018 |
| Jobbintro AS | Health & social care | 1989 |
| Johnny Eriksson AS | Health & social care | 1995 |
| Joon AS | Information & communication | 2022 |
| Jota Handel Ans | Wholesale & retail | 1992 |
| Jotan Markiser AS | Wholesale & retail | 2016 |
| Jul-Larsen AS | Construction | 2025 |
| Julianus Prosjekt AS | Financial services | 2000 |
| Juras Invest AS | Information & communication | 2023 |
| Just a Code AS | Information & communication | 2009 |
| Juve Invest AS | Professional & scientific | 2017 |
| Jan og Hege Raaen A/S | Real estate | 1967 |
| Jørgen Transport AS | Water & waste | 2019 |
| K Varehandel AS | Wholesale & retail | 2020 |
| K2 Nordic AS | Professional & scientific | 2026 |
| Kalabra AS | | 2010 |
| Kalupe AS | Construction | 2012 |
| Kamajo AS | | 2018 |
| Karljohansvern Eiendom AS | Real estate | 2001 |
| Karljohansvern Invest AS | Real estate | 2015 |
| Kaus Holding AS | | 2022 |
| Kausland Holding AS | | 2025 |
| KD Holdco AS | | 2026 |
| Kebet Holding AS | Real estate | 2023 |
| Keo Horten AS | Wholesale & retail | 2019 |
| Kg-Eiendoms Invest AS | Real estate | 2020 |
| Kiropraktorklinikken Horten Sykehus AS | Health & social care | 2002 |