A timber shed and caravan have been illegally sited on green belt land within the Shendish Manor estate.
Dacorum Borough Council issued an enforcement notice in February this year ordering for the residential use of land at Cocks Head Wood to stop.
Hardcore has also been laid for access.
An appeal against the notice was dismissed in July and council chiefs are now considering what further action they will take.
Council group manager for development management and planning Sara Whelan said: “As the deadline for completing the requirements of the enforcement notice have passed, an offence has been committed. As such we will decide on our next course of action to resolve this matter which may include legal proceedings.”