| Ridgeon Group Limited | Extraterritorial | 1931 |
| Ridgeon Holdings Limited | Financial services | 2016 |
| Ridgeon Properties Limited | Real estate | 1947 |
| Ridgeons Forest Products Limited | Extraterritorial | 1987 |
| Ridgeons Limited | Extraterritorial | 1989 |
| Russell-Hughes Evans CYF | Professional & scientific | 2020 |
| S J Chubb Transport Ltd | Transport & logistics | 2016 |
| Saer Felen Joinery Ltd | Manufacturing | 2021 |
| SAM Walker Communications Ltd | Professional & scientific | 2022 |
| Sandysike Builders Merchants Limited | Extraterritorial | 2000 |
| SAS Takeaway Limited | Hospitality | 2024 |
| Secure Solutions Anglesey Ltd | Administrative & support | 2023 |
| Serenity Beauty & Skincare Salon Ltd | Other services | 2009 |
| Shore to Summit Escapes Ltd | Hospitality | 2026 |
| SI1LLE Ltd | Real estate | 2025 |
| Solanum Medical Communications Limited | Professional & scientific | 2016 |
| Sonix Software Ltd | Administrative & support | 2014 |
| South Milford (Holdings) Limited | Extraterritorial | 2007 |
| Southwark Residential Limited | Hospitality | 1997 |
| Stompyshome Stud Limited | Agriculture & fishing | 2021 |
| Strawberry Farm Store Ltd | Wholesale & retail | 2024 |
| SW Newco Limited | Real estate | 2018 |
| Switched on Electrical & Renewables Ltd | Construction | 2025 |
| T Williams Roofing Ltd | Construction | 2025 |
| Tafarn PUB Group Ltd | Hospitality | 2025 |
| TAN Y Felin Limited | Hospitality | 2019 |
| TBS Building Supplies Ltd | Extraterritorial | 1978 |
| Telimôn CYF | Information & communication | 2019 |
| Terry Owen & Rhys Parry Plastering Ltd | Construction | 2024 |
| TG Hub Ltd | Wholesale & retail | 2023 |
| THE Amlwch Industrial Heritage Trust Limited | Education | 1997 |
| THE Coach House (Red Wharf Bay) Management Company Limited | Households | 2022 |
| THE Coffee HUT Llangefni Limited | Hospitality | 2026 |
| THE Llangefni (NO1) Limited Partnership | | 2014 |
| THE Timber Group Limited | Extraterritorial | 1992 |
| Theatr Prysor CIC | Arts & recreation | 2024 |
| TIP Top Tiling Ltd | Construction | 2026 |
| TOM Eves Ltd | Professional & scientific | 2015 |
| Transcentia Ltd | Professional & scientific | 2012 |
| TSJ Construction Ltd | Construction | 2014 |
| Tudur CYF | Information & communication | 2001 |
| TY Llwyd Lodges Limited | Hospitality | 2025 |
| Update Ltd | Manufacturing | 2025 |
| Uriah Woodhead & SON (Holdings) Limited | Financial services | 2020 |
| Uriah Woodhead & SON Limited | Extraterritorial | 1936 |
| W. J. Roberts Builders Merchants Limited | Transport & logistics | 1988 |
| W. O. Jones (Printers), Limited | Manufacturing | 1946 |
| W.D. Williams & Sons Ltd | Agriculture & fishing | 2003 |
| Warrior Spirit Health & Fitness Limited | Education | 2025 |
| William Hughes (Civil Engineering) Limited | Water & waste | 1973 |
| Williams & Goodwin, the Property People Limited | Real estate | 2002 |
| Woodruff Properties Limited | Real estate | 2020 |
| Y Golchdy Bach CYF | Wholesale & retail | 2021 |
| Ynys MON Properties Ltd | Real estate | 2025 |
| Zest Housekeeping Ltd | Other services | 2022 |