| Sentrum Tannlegekontor Farahani AS | Health & social care | 2012 |
| Sentrumsgården Snåsa AS | Real estate | 2021 |
| Sentrumsgårdene Steinkjer AS | Real estate | 1990 |
| Sersjantveien 11 Eiendom AS | Real estate | 2011 |
| Service & Support AS | Construction | 2023 |
| Setten Holding AS | Wholesale & retail | 2022 |
| Sevvis Holding AS | | 2019 |
| SG4EF AS | Real estate | 2022 |
| SH Gruppen Holding AS | Other services | 2022 |
| SHG Eiendom AS | Real estate | 2017 |
| Shootr AS | Professional & scientific | 2025 |
| Sirius Økonomi AS | Professional & scientific | 2021 |
| Sivilingeniør Eirik Nordvik AS | | 2019 |
| Sjem Holding AS | | 2023 |
| SJH Invest AS | | 2022 |
| Sjøfartsgata 10B AS | Real estate | 2019 |
| Sjøfartsgata 11 AS | Real estate | 2015 |
| Sjøfartsgata 15 AS | Real estate | 2015 |
| Sjøkanten Steinkjer AS | | 2001 |
| Sjøsia Legekontor Ans | Health & social care | 2000 |
| Skanska Husfabrikken AS | Manufacturing | 1996 |
| Skar & Lægran AS | Other services | 2016 |
| Skei & PT Da | Arts & recreation | 2011 |
| Skei Og Røsegg Samdrift Ans | Agriculture & fishing | 2000 |
| Skeidar Steinkjer AS | Wholesale & retail | 1995 |
| Skippergata 10 Eiendom AS | | 2005 |
| Skjeflo Sag Ans | Manufacturing | 1987 |
| Skjefte Barnehage AS | Education | 2005 |
| Skjefte Holding AS | | 2022 |
| Skjei Invest AS | | 2024 |
| Skjervold Blengsli Ans | Administrative & support | 2025 |
| Skjervø Kommunikasjon AS | Professional & scientific | 2026 |
| Skjevlo Gård Da | Agriculture & fishing | 2011 |
| Skogelva Kraftverk AS | Energy | 2014 |
| Skogkraft AS | Energy | 2009 |
| Skolegata 14-16 AS | Real estate | 2019 |
| Slatlem Steinkjer AS | Wholesale & retail | 2014 |
| Slipehuset AS | Manufacturing | 2012 |
| Smack Holding AS | Financial services | 2015 |
| Smart Grid Services SA | Professional & scientific | 2020 |
| Smart Media AS | Information & communication | 2014 |
| Smart Norway AS | Information & communication | 2014 |
| Smartbool Da | Information & communication | 2016 |
| Smash Invest AS | | 2020 |
| Sneppen Frisør AS | Other services | 2008 |
| Snota AS | Education | 2005 |
| Snåsa Naturstein AS | Mining & quarrying | 2013 |
| Solhøi Mekaniske AS | Manufacturing | 1995 |
| Solidbolig AS | Real estate | 2025 |
| Solvang Industrier AS | Financial services | 2004 |
| Solvit Industries AS | | 2024 |
| Sotberg Kjeldseth Invest AS | Wholesale & retail | 2018 |
| Spar-Bygg AS | Construction | 1984 |
| Spar-Bygg Utbygging AS | Real estate | 2004 |
| Sparbu Småbåthavn SA | Transport & logistics | 2021 |
| Spektro AS | Manufacturing | 2006 |
| Spero Eiendom AS | Real estate | 2015 |
| Spero Invest AS | Health & social care | 2011 |
| Spleislaget AS | Professional & scientific | 2024 |
| Sports-Ed Scandinavia Da | Education | 2007 |
| Sportshytta AS | Wholesale & retail | 1989 |
| Sprova Pukk AS | Mining & quarrying | 1999 |
| SS Bygg Og Service AS | Construction | 2019 |
| Ssa Steinkjer AS | Arts & recreation | 2020 |
| Stagent Eiendom AS | Real estate | 2022 |
| Stall Kringla AS | Arts & recreation | 2019 |
| Stall Skjevlo AS | Agriculture & fishing | 2025 |
| Star Advice Holding AS | Professional & scientific | 2013 |
| Star Investment AS | Professional & scientific | 2022 |
| Stasjonsdrift Even Berg AS | Wholesale & retail | 2022 |
| Stavrum Utbygging AS | Real estate | 2016 |
| Steffensen Utbygging AS | | 2026 |
| Steget Holding AS | Real estate | 2020 |
| Steigtind Invest AS | Real estate | 2015 |
| Steinkaret Scene AS | Information & communication | 2015 |
| Steinkjer Agenturforretning AS | Wholesale & retail | 1988 |
| Steinkjer Arrangement AS | Administrative & support | 2022 |
| Steinkjer Avisa AS | Information & communication | 1984 |
| Steinkjer Bad & Våtrom AS | Construction | 2018 |
| Steinkjer Bedehus AS | Real estate | 1960 |
| Steinkjer Bil AS | Other services | 1996 |
| Steinkjer Bil Eiendom AS | Other services | 1985 |
| Steinkjer Bil Holding AS | Other services | 2005 |
| Steinkjer Bilberging AS | Real estate | 1996 |
| Steinkjer Bilinnsamling Eiendom AS | Real estate | 1990 |
| Steinkjer Blikk AS | Construction | 2022 |
| Steinkjer Bokhandel AS | Wholesale & retail | 2014 |
| Steinkjer Brød & Cirkus AS | Hospitality | 2005 |
| Steinkjer by- Og Bygdeservice SA | Construction | 2000 |
| Steinkjer Bygg Og Montasje AS | Construction | 2016 |
| Steinkjer Byutvikling AS | Real estate | 2020 |
| Steinkjer Camping AS | Real estate | 1986 |
| Steinkjer Catering AS | Hospitality | 2024 |
| Steinkjer Dagligvare AS | Wholesale & retail | 2015 |
| Steinkjer Data AS | Information & communication | 2007 |
| Steinkjer Dyrebutikk AS | Wholesale & retail | 2005 |
| Steinkjer Dyreklinikk AS | Professional & scientific | 2010 |
| Steinkjer Eiendom AS | Real estate | 1998 |
| Steinkjer Fysikalske AS | Health & social care | 2009 |
| Steinkjer Gass AS | Wholesale & retail | 2006 |