Sir Wilson, a MP in the 1800s and the first president of the New Zealand Farmer's Union, named it after one of his favourite places in Scotland. He and his wife had five children with Lady Wilson leaving it to her daughters when she died.
Mrs Haylock also grew up there and returned later with a husband Owen and children after a stint in Palmerston North. She's been there since.
The home is in much the same state as when it was built with original wallpaper and hand-crafted furniture Sir James Wilson had shipped from England. Pieces of tapestry made by Lady Wilson still hang on the walls. Upstairs in one of the rooms is a hand-made cot the Wilsons brought back from England in 1924, the year before Mrs Haylock was born.
Lethenty was built in 10 months for 2000 using native timber including rimu matai and totara. "The timber in it is all heart timber. It's lovely rimu. It's got concrete piles which is quite good for 1915," Mrs Haylock said.
Ladies of Lethenty tells the story of the house and the family including the books and speeches which were written there.
The two-story house was designed by J H James and W T Higgins of Marton and the original plans sit in the Whanganui Regional Museum. It now has B heritage status.
"But the sad thing is we don't know who the builders were," Mrs Haylock said.
She said her grandparents would be proud to know it was still in the family.
A function to mark the home's centenary and the launch of the book is being held on September 6 at the Bulls Town Hall at 11am. Members of the public are welcome to attend.