Counties 1 Hertfordshire (formerly Counties 1 Herts/Middlesex and before that London 2 North West) is a tier 7 English Rugby Union league. It is organised by the London and South East Division Rugby Football Union and is the top-tier competition for clubs primarily in Hertfordshire together with others from parts of north-west London (that traditionally was encompassed by the historic county of Middlesex) and Essex. It was previously known as London 2 North West. After the restructuring of the English rugby union system ahead of the 2022–23 season, the league was renamed to Counties 1 Herts/Middlesex. Ahead of the 2025–26 season a decision was taken to split Hertfordshire RFU and Middlesex RFU clubs, with Middlesex teams moving on a level transfer to Counties 1 Middlesex while club 2XVs were introduced to the league. Brunel University are the current champions.

Each year the two Hertfordshire clubs in this division with the best record against other Hertfordshire clubs also take part in the Hertfordshire Presidents' Cup, the highest level county cup competition in Hertfordshire. Promoted teams typically go up to Regional 2 Thames while relegated teams drop to Counties 2 Hertfordshire.

The champions are promoted to Regional 2 Thames while one or two teams are relegated to Counties 2 Hertsfordshire. Since 2025–26 the league includes Essex clubs precluded from competing in Essex Rugby leagues which don't permit reserve sides in first XV leagues. The season runs from September to April and comprises eighteen rounds of matches, with each club playing each of its rivals, home and away. The results of the matches contribute points to the league as follows:

Departing were Cheshunt promoted to Regional 2 Anglia. Also leaving on a level transfer to Counties 1 Essex were Eton Manor II (5th) and Southend Priors (9th). There was no relegation.

This was the first season with the league containing mainly Hertfordshire RFU clubs. Leaving on a level transfer to the newly re-formed Counties 1 Middlesex league were Chiswick (9th), Ealing Trailfinders 1871 (4th), Finchley (3rd), Ruislip (6th) and Old Streetonians (5th). Also departing were Brunel University promoted to Regional 2 Thames while Hackney (11th) and Datchworth (12th) were relegated to Counties 2 Middlesex and Counties 2 Hertfordshire respectively.

Departing were London Scottish Lions promoted to Regional 2 Thames, and Enfield Ignatians and Hampstead relegated to Counties 2 Herts/Middlesex. Joining were Brunel University and Ealing Trailfinders 1871, promoted from Counties 2 Herts/Middlesex, together with Fullerians, relegated from Regional 2 Thames.

Departing were Hemel Hempstead and Grasshoppers, promoted to Regional 2 Thames. There was no relegation. Joining were Cheshunt and London Scottish Lions, both promoted from Counties 2 Herts/Middlesex.

This was the first season following the RFU Adult Competition Review. The league was substantially similar to London 2 North West with eight of the teams competing in the previous season, while the top four moved to Regional 2 Thames or Regional 2 Anglia. They were replaced with the top three from London 3 North West and Chiswick on a level transfer from London 2 South West.