In Thames-Coromandel, 26.6 per cent of its population is aged over 65.
By contrast, only 11.2 per cent of Hamilton's population is of retirement age.
While most territorial authorities will not experience natural decline (more elderly than children) until 2040, Thames-Coromandel was already in decline.
New Zealand's leading demographer Dr Natalie Jackson said the country was going to see the end of population growth in the next few years.
"In parts of [the region] like Thames-Coromandel and Hauraki for example, you're going to deal with a declining population, a population that is not growing," she said.
"Hospitals in the past were built for young people and babies and not built for our elderly so we need to start considering that now."
Waikato District Health Board (DHB) chairman Bob Simcock said it was important for the region to understand the implications of an ageing population. "Already a number of communities are losing population and struggling to maintain services, so I think it's important for people to realise that."
"We're lucky in a sense that the city [Hamilton] is going to deliver us a younger population for longer than other parts of New Zealand so we will still have a competitive workforce but it's particularly about how we're going to deliver those services out to the rural areas, I think that's going to be a big challenge for us."
Simcock said it was critical for Waikato DHB to work with local councils.
The health board will meet with councils in the next few weeks to discuss what the statistics mean for the region.
"Particularly in the more remote communities, which are already a challenge to us, we still have an obligation to deliver services and we need to discuss how do we do that," he said. "While we have sort of known this stuff I think there's a lot of wishful thinking that somehow or another we can stop it or whether immigration will change it and in really small towns you can, it will make a difference but what this shows is that it's not challengeable, it's inevitable."
There are currently 650,000 people aged over 65 and by late 2040, that figure will rise to 1.3 million.
"This year alone 45,000 baby boomers will turn 65, the number rising every year to peak at around 60,000 per year in the mid 2020s," Jackson said.
Older people are working longer, in 1996 under 9 per cent in the overs  were employed and now 20 per cent of the overs are employed but although they're working longer, they're not going to solve New Zealand's forthcoming labour shortages."
Jackson said the region could be saved by Hamilton's youthful population. Hamilton city was where the region could look to draw its workforce from, she said. "Half of [Hamilton's] Maori population is under the age of 24 so there is huge potential for supply as they take over the labour force roles," she said.
This media item was current at its release date. The facts or figures it contains may have changed since its original publication.