| Northamptonshire People First Ltd | Other services | 1995 |
| Northants Land Drainage Contractors Limited | Other services | 1960 |
| Oakway Nursery Ltd | Education | 2009 |
| Offaplan Limited | Manufacturing | 1981 |
| Old Stratford Plumbing Ltd | Construction | 2013 |
| Omnisave Limited | Transport & logistics | 1983 |
| Opulent Northants Ltd | Real estate | 2025 |
| Orbit Tyre Co. Limited | Extraterritorial | 1962 |
| Overseas Building and Engineering Limited | | 1979 |
| P a Green Brickwork Limited | Construction | 2005 |
| P Morgan Consultancy Services Ltd | Professional & scientific | 2010 |
| P.J.E. Carpentry & Kitchens Limited | Construction | 2006 |
| Parc Design Solutions Limited | Professional & scientific | 2007 |
| Parcelroute Limited | Transport & logistics | 1987 |
| Pattishall Properties Limited | Real estate | 1963 |
| Paul Brightwell Limited | Households | 2008 |
| Pause for a While Photography Ltd | Other services | 2007 |
| PFD Consulting International Limited | Professional & scientific | 2006 |
| Phillips & Sons (Rushden) Limited | Real estate | 1940 |
| Phoenix Executive Services Limited | Professional & scientific | 1957 |
| PJG Solutions Ltd | Information & communication | 2004 |
| Plus One Software Limited | Professional & scientific | 1991 |
| Poole Construction (Northants) Limited | Administrative & support | 2007 |
| Postensioned Structures (UK) Ltd. | Construction | 1993 |
| Prestige Developments (Park Homes) Limited | Administrative & support | 2001 |
| Prestige Plastics Limited | Manufacturing | 2001 |
| Pro-Street Cycles Limited | Wholesale & retail | 2003 |
| Profile Housing Limited | Construction | 2006 |
| Profitable Learning Limited | Information & communication | 1992 |
| Promote - IT ! Limited | Information & communication | 1998 |
| Prosaw Limited | Wholesale & retail | 1973 |
| R & S Shires (Farmers) Limited | Agriculture & fishing | 1961 |
| R C LEA Limited | Construction | 2005 |
| R Payne Limited | Construction | 2005 |
| RB Creative Strategy Ltd | Professional & scientific | 2023 |
| Reedglen Limited | Professional & scientific | 1982 |
| Regent Commercial Services Limited | Professional & scientific | 2011 |
| RH Building Services Limited | Construction | 2006 |
| Risk Consulting (Davidrsmith) Limited | Financial services | 2007 |
| Rollasons Limited | Professional & scientific | 1998 |
| Rong DA Ltd | Hospitality | 2024 |
| Root Cause Solutions Ltd | Professional & scientific | 2007 |
| RS Consultants Limited | Real estate | 1999 |
| RST Safety Systems Ltd | Administrative & support | 2005 |
| Sadler Electrical Limited | Construction | 2001 |
| Sadler Solar Limited | Construction | 2001 |
| Saints Together Christian Services - UK | Other services | 2008 |
| Sally Armstrong Limited | Hospitality | 2005 |
| Sanders and Sanders Limited | Manufacturing | 1938 |
| Sharman Plant Limited | Construction | 2002 |
| SHE Products Co. Limited | Manufacturing | 1957 |
| Shippio Ltd. | Transport & logistics | 2009 |
| Simpson's Apartments Ltd | Hospitality | 2015 |
| Sino Realtors (UK) Ltd | Real estate | 2025 |
| Snaffles Equine Nutrition Limited | Wholesale & retail | 2006 |
| Softal Electronic | | 1995 |
| Sonifex Limited | Manufacturing | 1983 |
| Sparkwise Limited | | 1979 |
| Spectrum Chemicals Limited | Manufacturing | 1983 |
| St.Edmunds Garage Limited | | 1960 |
| Stanpart Components Limited | | 1978 |
| Star Self-Store Kettering Ltd | Professional & scientific | 1974 |
| Stoke Lodge Farm Limited | Agriculture & fishing | 1963 |
| Stonehaus Limited | Construction | 2006 |
| Sunair (Corby) Limited | Real estate | 1981 |
| T and G Decorators Limited | Construction | 2006 |
| T. G. Lewis Limited | Manufacturing | 1981 |
| T. J. Beeden and R. Berry | | 1989 |
| T.Chalmers Ltd | Construction | 2006 |
| Tate Brothers (Farthingstone) Limited | Administrative & support | 1958 |
| TGN Hosting Limited | Information & communication | 2006 |
| THE Iris Project | Education | 2007 |
| THE Outdoor Play Company Limited | Professional & scientific | 2005 |
| Thibekka Limited | Wholesale & retail | 2019 |
| Thrapston Market Company | Other services | 1981 |
| Timer Solutions Ltd | Transport & logistics | 2013 |
| Tingdene Lettings (Commercial) Ltd | Other services | 2019 |
| Tingdene Lettings Limited | Real estate | 2014 |
| TJH Engineering Ltd | Professional & scientific | 2007 |
| Towcester Tots Day Nursery Limited | Education | 2005 |
| Trafford Engineering Limited | Extraterritorial | 1966 |
| Tranex Telecommunications Limited | Information & communication | 1978 |
| Tred Gold Kettering Ltd | Construction | 2007 |
| Truckwright Limited | Transport & logistics | 2001 |
| Turnerborg Limited | Professional & scientific | 2006 |
| Tyrolit Limited | Wholesale & retail | 1974 |
| UC Sales Ltd | Wholesale & retail | 2025 |
| UK Pet Food | Other services | 1995 |
| Vace Ltd | Manufacturing | 2005 |
| Venture Aerospace Ltd | Professional & scientific | 2006 |
| Victoria Street Flats Management Company Limited | Households | 2006 |
| Vitacroft Limited | Information & communication | 2008 |
| Vulcan Fire Training Co Ltd | Education | 2005 |
| Wakefield Farms Limited | Agriculture & fishing | 1983 |
| Warehouse Apartments Limited | Administrative & support | 2003 |
| Waterwise Leak Detection Ltd | Construction | 2004 |
| Weatherbys Bank Limited | Financial services | 1994 |
| Weatherbys Ltd | Information & communication | 1953 |
| Weetabix Trustee Limited | Professional & scientific | 1993 |
| Wider Fit Shoes Limited | Wholesale & retail | 2004 |