Those who stay in areas including Timaru, the West Coast and Northland rated top in spirits, compared with Marlborough which was least happy.
Widows, widowers and married people were also happier than those who are divorced or single, while those living without children were much happier than those living with youngsters.
Pacific Islanders were the happiest of all ethnicities, while Maori were the second happiest.
Around 26,250 people aged 18 and over were surveyed between late June 2010 and last December.
Age Concern Counties Manukau chief executive Wendy Bremner, 51, said the secret to happiness was contentment and the idea of helping others.
"Lots of the older people are involved in activities that are for others. So many of them do things for their family and their grandchildren and community groups and organisations and ... when you do things for other people, you get more joy out of that than when you do things for yourself."
Mrs Bremner said most of those volunteering for Age Concern - some of whom are in their 90s - were also involved in other volunteering efforts.
"Younger generations have a lot more pressure to get more and do more and it's about the attainment that they think that's going to get them happiness, instead of the joy.
"I think the secret to happiness is more about contentment. Enjoying the moment. You've got to be able to enjoy the now.
"Older people are able to do that - they're not thinking about what school I'm going to, what am I going to study, what job am I going to get, am I going to have kids, what kind of house am I going to buy."
Mrs Bremner said she wasn't surprised that women were happier than men, as many women had strong friendships with other women - something many men did not have.
Northland man Rob Bryington, who lives in Kerikeri, said the laidback lifestyle and sunny weather was what helped keep people in his home town in good spirits.
"I think the weather plays a big part to that. We've always got good weather and it's always hot up here.
"People in the shops and supermarkets are very easygoing. You do get the odd grumpy one, but usually people are quite happy here."
Mr Bryington, 62, works as the manager at Kerikeri Homestead Motel.
He said he had a fair idea of why older people had a reason to smile.
"Well there's golf isn't there?"
Asked if he enjoyed golf, he laughed: "No, I don't have time to play golf - I'm working."
GOOD LIFE
Happiest
* 65 or over
* Those in Timaru, Oamaru, Taranaki, Northland
* Retirees and homemakers
* Pacific Islanders and Maori
* Homeowners with no mortgage
* Widowers and married people
* Those living without children
Not so happy
* People aged 45 to 49
* Those in Marlborough
* Renters or those paying a mortgage
* People who are divorced
* Those living with children
