His Majesty's Inspectorate of Constabulary and Fire and Rescue Services (HMICRFS) published its latest findings on the force's performance.
It said the force must do better when it investigates crimes, improve the way it protects vulnerable people and how it responds to the public.
Roy Wilsher, who led the inspection, said: "I recognise the current leadership's work on improvement, but I have some concerns with aspects of the performance of Derbyshire Constabulary in keeping people safe and reducing crime.
"I don't underestimate the difficulty caused by the constabulary's legacy issues, such as a lack of policy, governance and performance scrutiny, but there are areas where the force still needs to improve.
"These are the findings I consider most important from our assessments of the force over the past year."
"This means investigation outcomes may not always be appropriate and opportunities to bring offenders to justice may be missed.
"We spoke to many staff who said they felt disconnected from the organisation.
"The constabulary hasn't given the workforce inclusion training for many years, although now it has plans to do so. Staff need to know what is expected of them, to feel included and make sure the public are treated fairly."
"It has made improvements in recording crime, protecting children online and investigating missing people and these improvements were made following our observations about these critical areas," he said.