Figures collected by GPs show that in Telford & Wrekin, there are 1,130 people over 65 who have been diagnosed with some form of dementia. But estimates by the NHS, based on the age profile and gender of patients, suggest that the real figure may be 1,780.
That means an estimated 650 pensioners living with a debilitating illness that has not been formally recorded by their doctor.
And the same figures show that in Shropshire there are 3,468 people over 65 who have been diagnosed with some form of dementia but based on the age profile and gender of patients, the NHS suggests the real figure could be closer to 4,915.
The figures are being collected in response to the Prime Minister's Challenge on Dementia set up by the previous PM, David Cameron.
The Department of Health wants GP surgeries in England to increase the rate of diagnosis. The target was for at least two thirds of the estimated number of people with dementia to be diagnosed by March 2015.
The latest data, for April this year, shows that the diagnosis rate for the whole of England is 67.3 per cent but area to area this ranges from 41 per cent to 90 per cent. Shropshire is beating the national target with a rate of 70.6 per cent.
The Royal College of General Practitioners said that doctors realised the importance of spotting the signs of dementia early but in some circumstances might delay making a formal diagnosis in the interests of patients and due to pressure on services to support them.
Professor Helen Stokes-Lampard, chair of the RCGP, said: "There may be some situations where GPs might validly consider it in the best interest of the patient to delay seeking a formal diagnosis, especially in the early stages of the condition if there is minimal adverse effect on daily living and functioning and where patients do not want to be labelled.
"This decision might also be influenced by GPs knowledge of the local availability of assessment and treatment services, which may be insufficient to meet demand."
What is dementia?
Dementia can affect people at any age and across England 456,000 people have been diagnosed.
The Alzheimer's Society said that getting a diagnosis allows people with dementia to access emotional, practical, legal and financial advice, as well as any support and treatment available.
The society's senior policy officer, Andrew Boaden, said: "Dementia diagnosis rates vary significantly from place to place, which is concerning.
"Alzheimer's Society research shows that over a third of people with dementia in the UK don't get a formal diagnosis, and we believe everyone with dementia has a right to know.
"With the number of people with dementia set to reach 1 million by 2021, the Government and the NHS must do more to address this issue."
Last month, the chairman of a dementia campaign group in Shropshire called to more support to be offered to those affected.
George Rook, of the Shropshire Telford and Wrekin Dementia Action Alliance, said: "There will always be people who either do not want to be assessed or who are told by their doctor that here is no point in having a diagnosis. There is indeed a higher rate of diagnosis in Shropshire, and T&W are working to address this.
"But the biggest challenge is to get some GPs to change their attitudes and to encourage people to get diagnosed. Almost everyone who is diagnosed is relieved to know, as it explains the symptoms they have been experiencing for some years.
"And a diagnosis allows you to access some services, such as support from the Alzheimers Society, and in many cases medication which reduces the symptoms. There is still terrible fear and stigma attached to dementia in our communities, including our doctors."
Rachel Wintle, Alzheimer’s Society dementia support manager for Shropshire said: “There are many reasons why people might not get a dementia diagnosis and these can include a lack of understanding about the benefits of getting a diagnosis and stigma that can still be associated with dementia. Every person with dementia is different and can experience different symptoms. Once diagnosed though, people with dementia will be better prepared to manage their symptoms.
"A diagnosis can also help access financial benefits such as a reduction in council tax in some cases or a carer receiving carer’s allowance. This can help people affected by dementia bear the financial load as we hear all too often that they are forced to spend large amounts of money on accessing home care or care homes fees. If you’re concerned about your memory or think you might already have a form of dementia then please talk with your GP about getting a diagnosis and the support out there."
For more information and help contact Alzheimer’s Society on 01952 250 392, alternatively information is available from Shropshire Dementia Action Alliance on 01543 255955 or Age UK