| Siomac Ltd | Financial services | 2020 |
| Sirrod Commercial Limited | Hospitality | 2003 |
| Skek Engineering Ltd | Manufacturing | 2019 |
| Skiinn Limited | Transport & logistics | 2020 |
| Skinworkz Beauty Ballymena Laser Ltd | Other services | 2025 |
| Skinworkz Beauty Limited | Other services | 2018 |
| Slemish Barn Ltd | Hospitality | 2016 |
| Slemish Building Contracts Ltd | Construction | 2018 |
| Slemish Business Hub Limited | Professional & scientific | 2020 |
| Slemish Environmental Services Ltd | Water & waste | 2026 |
| Slemish EYE Clinic Limited | Health & social care | 2019 |
| Slemish Ltd | Administrative & support | 2013 |
| Slemish Stone Limited | Wholesale & retail | 2022 |
| Slemish Tractors Limited | Manufacturing | 2023 |
| Slemish View Ltd | Financial services | 2025 |
| Slider Properties Ltd | Real estate | 2025 |
| SLS Developments Ltd | Construction | 2018 |
| SM Sleep Solutions Ltd | Health & social care | 2025 |
| SMA Agencies Limited | Health & social care | 2011 |
| SMA1 Limited | Real estate | 2025 |
| SMC Health & Fitness Limited | Arts & recreation | 2020 |
| Smith's Engineering Works (Northern Ireland) Limited | Manufacturing | 1969 |
| Smiths Secure Ltd | Manufacturing | 2016 |
| Smjc Properties Ltd | Real estate | 2024 |
| Smyth & Gibson Investments Limited | Financial services | 2011 |
| Smyth & Gibson Shirtmakers Limited | Manufacturing | 2007 |
| Smyth Farms Ltd | Agriculture & fishing | 2025 |
| Smyths Wallpaper & Paints Ltd | Wholesale & retail | 2019 |
| Smythscatering Ltd | Hospitality | 2025 |
| Snaffle Snacks Ltd | Manufacturing | 2017 |
| SNG Motors Ltd | Wholesale & retail | 2018 |
| SNW Developments Limited | Real estate | 2024 |
| SOK Agri Ltd | Agriculture & fishing | 2025 |
| Solarflexx Group Ltd | Construction | 2026 |
| Solve Engineering Ltd | Information & communication | 2019 |
| Sonatiks Ltd | Wholesale & retail | 2023 |
| Sontac Ltd | Information & communication | 2018 |
| Sooo CIC | Manufacturing | 2021 |
| Source Electrical (Ireland) Ltd | Construction | 2023 |
| Space Wellness Ltd | Health & social care | 2023 |
| Spat Retail Ltd | Wholesale & retail | 2018 |
| SPB Belfast Ltd | Administrative & support | 2010 |
| Specialist Trails Ltd | Construction | 2024 |
| Sped Trading Ltd | Health & social care | 2016 |
| Speedy Energy Solutions Ltd | Manufacturing | 2025 |
| Spirit Utilities Limited | Administrative & support | 2006 |
| Splippers.Com Ltd | Information & communication | 2025 |
| Sportsphereni Ltd | Education | 2024 |
| Sprayfiltersni Limited | Energy | 2023 |
| Spring Meadow Investment Ltd | Financial services | 2021 |
| Springhill Services (NI) Limited | Households | 2021 |
| Squeak & Bistos Ltd | Hospitality | 2026 |
| SRJ Davison Limited | Manufacturing | 2017 |
| ST Colmcille's After School Club | Education | 2017 |
| Star Appliances Ltd | Water & waste | 2023 |
| Starling Entertainments Corporate Limited | Arts & recreation | 2023 |
| Starling Entertainments Limited | Other services | 2015 |
| Station House Management Company (Ballymoney) Limited | Households | 2022 |
| Steelx Structures Ltd | Construction | 2020 |
| Steelx Systems Ltd | Manufacturing | 2023 |
| Stemfab Ltd. | Manufacturing | 2017 |
| Stephen Gibson Paving Limited | Construction | 2016 |
| Stephen Kerr Designs Ltd | Professional & scientific | 2025 |
| Stephen's Property Management Ltd | Administrative & support | 2025 |
| Stephens Catering Equipment Company Limited | Wholesale & retail | 1975 |
| Steven Davis Plumbing Ltd | Construction | 2026 |
| Steven Lowry Memorial Trust | Other services | 2013 |
| Stevenson & Wilson | Professional & scientific | 2023 |
| Stevenson and Company, | Real estate | 1978 |
| Stevenson Packaging Ltd | Wholesale & retail | 2015 |
| Stewart (NI) Limited | Hospitality | 2014 |
| Stewart Maze Ltd | Wholesale & retail | 2024 |
| Stock Tech IT Ltd | Administrative & support | 2023 |
| Stoneridge Financial Ltd | Real estate | 2024 |
| Stonetec Wind Ltd | Energy | 2015 |
| Stormtecmarine Limited | Wholesale & retail | 2009 |
| Stovetech (N.I.) Limited | Manufacturing | 2017 |
| Straid Holdings Limited | Financial services | 2021 |
| Strand House Apartments Ltd | Households | 2026 |
| Strathview Farm Ltd | Agriculture & fishing | 2015 |
| Strawbridge Limited | Professional & scientific | 2024 |
| Streetly Ltd | Information & communication | 2025 |
| Strength & Dignity Ltd | Wholesale & retail | 2024 |
| Structural Fire Solutions Limited | Construction | 2018 |
| Studio B57 Ltd | Professional & scientific | 2021 |
| Sub-E Solutions Ltd | Construction | 2018 |
| Sublime Cattle Bedding Ltd | Extraterritorial | 2014 |
| Subway (Fairhill) Limited | Hospitality | 2008 |
| Success KA Limited | Real estate | 2024 |
| SUE RRR Ltd | Health & social care | 2022 |
| Sugar FX Ltd | Wholesale & retail | 2017 |
| Sunny Nail & Spa Ballymena Ltd | Other services | 2024 |
| Sunny's (Ballymena) Ltd | Hospitality | 2018 |
| Sunnys (Properties) Ltd | Real estate | 2020 |
| Sunset IT LLP | | 2025 |
| Superclean Pressure Washers Ltd | Wholesale & retail | 2026 |
| Supplio Technologies Ltd | Information & communication | 2026 |
| Suredry-Ni Limited | Construction | 2026 |
| Susan J. Davidson Ltd | Other services | 2021 |
| Sustainable Paws Ltd | Wholesale & retail | 2025 |