| Steinkjer Golfsenter AS | Arts & recreation | 2021 |
| Steinkjer Gravstell AS | Other services | 2022 |
| Steinkjer Hagesenter AS | Wholesale & retail | 1987 |
| Steinkjer Hagesenter Eiendom AS | Real estate | 1965 |
| Steinkjer Handelspark AS | Real estate | 1990 |
| Steinkjer Havnelager AS | Real estate | 1970 |
| Steinkjer Holding AS | Wholesale & retail | 2016 |
| Steinkjer Hørsel AS | Health & social care | 2018 |
| Steinkjer Kiropraktorsenter AS | Health & social care | 1996 |
| Steinkjer Kornsilo SA | Manufacturing | 1939 |
| Steinkjer Kulturbygg AS | Construction | 2017 |
| Steinkjer Lakkering AS | Other services | 1999 |
| Steinkjer Liftutleie AS | Administrative & support | 2013 |
| Steinkjer Mekaniske AS | Manufacturing | 1995 |
| Steinkjer Militærutsalg Da | Wholesale & retail | 1995 |
| Steinkjer Motorsenter AS | Other services | 2022 |
| Steinkjer Padelsenter AS | Real estate | 2016 |
| Steinkjer Pizza Og Grill AS | Hospitality | 2020 |
| Steinkjer Psykologsenter AS | Health & social care | 2005 |
| Steinkjer Skidrift AS | Arts & recreation | 2001 |
| Steinkjer Skredder AS | Other services | 2024 |
| Steinkjer Tak AS | Construction | 2018 |
| Steinkjer Taxi AS | Transport & logistics | 2019 |
| Steinkjer Taxilag SA | Transport & logistics | 2023 |
| Steinkjer Tomteselskap AS | Real estate | 1968 |
| Steinkjer Trafikkskole AS | Education | 2016 |
| Steinkjer Uldvarefabrikk AS | Real estate | 1958 |
| Steinkjer Ur Og Smykker AS | Wholesale & retail | 2009 |
| Steinkjer Utvikling AS | Professional & scientific | 1991 |
| Steinkjer Varme Og Hyttesenter AS | Wholesale & retail | 2008 |
| Steinkjer Vaskeri AS | Other services | 2013 |
| Steinkjer Vulk AS | Wholesale & retail | 1994 |
| STEINKJER24 AS | Information & communication | 1981 |
| Steinkjeradvokatene Ans | Professional & scientific | 1988 |
| Steinkjerbakken Osteopati AS | Health & social care | 2004 |
| Steinkjerbygg AS | Real estate | 1941 |
| Steinkjerfestivalen AS | Arts & recreation | 2000 |
| Steinkjerfestivalen Event AS | Administrative & support | 2022 |
| Steinkjerhallen AS | Arts & recreation | 1980 |
| Steinkjerhus AS | Real estate | 2002 |
| Steinkjerstein AS | Mining & quarrying | 2017 |
| Steinkjervassdraget Fellesforvaltning SA | Real estate | 2023 |
| Steinmo Holding AS | | 2021 |
| Stevi AS | | 2026 |
| Stian Kalstad Holding AS | | 2018 |
| Stima Holding AS | Real estate | 2020 |
| Stitko AS | Education | 2023 |
| Stod Bygdaverksted Da | Manufacturing | 1995 |
| Stod Maskinlag SA | Agriculture & fishing | 2000 |
| Stod Sambeitelag SA | Agriculture & fishing | 1952 |
| Stod Samfunnshus Og Bygdeutvikling SA | Real estate | 2004 |
| Stodveitjan AS | Professional & scientific | 2013 |
| Stornes Transport AS | Transport & logistics | 1985 |
| Storstad Investments AS | Professional & scientific | 2015 |
| Strandvegen 1 Eiendom AS | Real estate | 2018 |
| Straxbo Boliger AS | Construction | 2026 |
| Streel Holding AS | | 2026 |
| Strøm Taxidrift AS | Transport & logistics | 2022 |
| Studio Albin AS | Professional & scientific | 2009 |
| Støa Holding AS | | 2025 |
| Støvik Kjølstad AS | Information & communication | 2014 |
| Subb Invest AS | | 2024 |
| Summit Invest AS | Financial services | 2005 |
| Sunnan Grendehus SA | Other services | 1964 |
| Susegg Service Og Salg Ans | Other services | 2002 |
| Svartøya Eiendom AS | Real estate | 2025 |
| Svein Jarls Gate 12 AS | Real estate | 2008 |
| Svein Jarls Gate 13 AS | Real estate | 2021 |
| Svein Jarls Gate 3 AS | Real estate | 2021 |
| Svein Jarlsgt. 2 AS | Real estate | 2022 |
| Sveinung Green AS | Wholesale & retail | 2004 |
| Svit AS | Professional & scientific | 2015 |
| Swift Invest AS | Financial services | 2005 |
| Synergo AS | Education | 1991 |
| Steinkjer Rådhus AS | Real estate | 1972 |
| Så Som Så AS | | 2025 |
| Sør-Beitstad Barnehage SA | Education | 1995 |
| Sørlie Musikksenter AS | Wholesale & retail | 1998 |
| Sørsia Minilager AS | Real estate | 2019 |
| T.Bratberg AS | Construction | 2026 |
| T:Lab AS | Professional & scientific | 2003 |
| T:Lab Capital AS | Professional & scientific | 2017 |
| Tamo Invest AS | Real estate | 2025 |
| Tanem Møller AS | Health & social care | 2025 |
| Tannlege Ammar Omar Mohammed AS | Health & social care | 2020 |
| Tannlege Håvard Moen AS | Health & social care | 2005 |
| Tannlege Petter Risan Granlund AS | Health & social care | 1999 |
| Tannlege Rune Kvaran AS | Health & social care | 2005 |
| Tantrasexolog AS | Education | 2023 |
| Taraldsen Eiendom AS | Real estate | 1988 |
| Tarandro AS | Professional & scientific | 2017 |
| Tasty Steinkjer AS | Hospitality | 2017 |
| TB Verkstedsenter AS | Other services | 2012 |
| TCS Holding AS | | 2020 |
| Tech Norway AS | Information & communication | 2023 |
| Technify AS | Professional & scientific | 2023 |
| Teknor System AS | Construction | 1990 |
| Tekvyn AS | Information & communication | 2025 |
| TEL1 AS | Professional & scientific | 2019 |
| Telas AS | | 2024 |