Acting chief executive Sian Forster said St George's gave them unprecedented flexibility and space, combined with playing fields and a swimming pool.
"This is so wonderful for us at the Y, and it's the perfect outcome for Wanganui. We will be preserving this outstanding heritage site for the future benefit of the whole community.
"We look forward with a great deal of excitement to welcoming all our existing community partners into our new home, together with all the families and schools that are already part of the YMCA story." Ms Forster said.
The school buildings sold to the Y include the main school block, former dormitories, classrooms, library, kitchen, new administration building, chapel, toilet blocks and staff living quarters. A large in-ground pool, playing fields and tennis courts were also included in the sale.
Mr McGregor said the Y in Wanganui had enjoyed the support of the entire community during the past 100 years.
The YMCA plans to make the move into St George's towards the end of the year and will publicise a variety of activities and events to celebrate what one staff member calls "a thrilling and exciting challenge".
The big move from the present administration headquarters at Park Place will finally go ahead in mid-January 2013.
A move which would be a mammoth task, Ms Ryder said as she pointed to stacks of boxes already stacked, sealed and ready to go.
The YMCA (the Young Men's Christian Association) is a worldwide organisation, which began in New Zealand in 1855 and quickly became a pioneer of physical fitness in young men with camps, walks and games.
During World War I and II the YMCA supported New Zealand soldiers.
However, since the 1980s, the association has expanded into helping all young people, including supporting the disabled, assisting children at risk with the law, offering educational opportunities and providing counselling services.
In 1955, two local families, the of fun and learning for youth
Good core values are what keep you together in a rapidly changing world, as is being able to change with the physical and financial circumstances of the times.YMCA Central President Rowan Phillips and the Mackintoshes of Aotea Station, donated land to the Wanganui YMCA for a children's adventure camp, which became The Raukawa Adventure Camp.
The association underwent a huge restructure in the 1990s, and Ms Ryder remembers it well.
"I was employed in the Health and Fitness Centre, teaching Aerobics and running the under-5s gym sessions."
Sadly the association was struggling financially and its Wilson St premises faced closure, she said.
To save the day, petitions were drawn up, and students and staff rallied together to get members and the community's support.
Even though enormous support was shown, it wasn't enough to save Wilson St and the YMCA was forced out, Ms Ryder said.
"It was time to diversify, and we did."
At the new premises in London St, family and friends knocked out and rebuilt walls, painted, cleaned and created spaces for offices and a children's gym.
"And we were back in business, even though it was with a much smaller staff and venues ... better than nothing."
The modern YMCA has made huge progress, because once the focus was solely on physical activity only and restricted to young men.
"Now it is for everyone from babies through to adults, girls, boys, men and women."
As well as the many fitness classes, holiday programmes and Oscar (after-school programmes), there are now 23 educational course available.
These include:
Learning for Life, Young Parents Wanganui, furniture making, meat processing, mechanical engineering, employment-focused training, youth literacy learning, mothers and pre-schoolers and workplace literacy.
The Y is one of Wanganui's biggest employers, making it a lynch-pin of the community.
President Rowan McGregor remembers vividly, as a boy, heading off to Raukawa Camp.
He remembers swimming in the river, the mudslides, the flying fox and scraping the spuds for dinner.
He believes the aims of the Y today are as important as they ever were.
"Good core values are what keep you together in a rapidly changing world, as is being able to change with the physical and financial circumstances of the times."
Walking through the doors into the holiday programmes over the past two weeks, whether it be at St George's or the Wanganui East complex on the corner of Hakeke St, you know the children inside are going to be absorbed and happy.
For each activity is carefully planned, from the materials needed if it's a craft endeavour, to the food, whether it be a cooking exercise or a special lunch for a group of small cowboys and a few tiny Indians.
The team leaders are an inspired bunch who really enjoy their young charges and love to help them have a great time.
Ms Ryder said even though she was immersed in administration these days, she still tried to get around the holiday traps and mingle with the kids at least twice a week
"I love being with the kids. I always did. I used to love organising and teaching ... children are so rewarding, and we all feel like that here."