Nearly 400,000 people are unaware they have dementia, because they or their loved ones do not spot the tell-tale signs and symptoms.
To mark World Alzheimer's Day, the Government wants to help raise awareness about the condition, which affects 670,000 people in the UK.
The number of people with Alzheimer's is expected to double over the next 30 years.
Prime Minister David Cameron said: "Dementia is a devastating disease that puts enormous strain on people and their families.
"Shockingly, nearly 400,000 people are unaware that they have the condition and so we want to make sure more people know what dementia is and how to spot those tell-tale signs."
The campaign has the support of several famous faces including Fiona Phillips, the Alzheimer's Society ambassador whose parents both had dementia.
She said: "If you think a loved one is showing the signs of dementia, it's so important to take that first step and talk to them about it.
"There are things you can do to help. Treatments can work well for people, but early diagnosis also means you can plan and get help, instead of doing everything in a rush."
A Bristol care home is also encouraging people to talk about the condition, as part of an innovative project to help residents cope.
Grove Care, a nursing home in Winterbourne, has built a model of a fifties village to help residents remember their past.
'Memory Lane' is complete with a traditional greengrocer, post office, bar and even a vintage phone box with original features.
Pat Deverell, who lives at the home, said: "There's a lot of things that it triggers off in your memory and that is good because it alters your life if you remember things. It's really important."
It is hoped the facility will also benefit friends and family, creating an environment which stimulates conversation and improves the time spent together.
Chris Taylor, the care home’s senior manager, said: "For a family member it can be quite challenging to find topics to talk about, but this provides them with talking points.
"I would also like to think it makes quite a nice pleasant place to sit outside, it's very important not to spend so much time inside."
At Memory Lane the residents can wander around as they please, walking in and out of the shops and pub, reading the replica newspapers and handling the souvenirs.
In doing so, it is hoped families and friends of those with dementia will be able to connect to their loved one, even if just for a moment.
