To mark the milestone, centenarian Maud Butler and her daughter Jean knitted more than 100 wool hats for premature babies, which will be donated to Northampton General Hospital.
Maud was treated to a surprise party and a generous buffet at St Anne's residential care home in Kettering on Monday.
"I knitted the hats with my mum after the home was asked if they would make them for the hospital," said Jean.
"But no-one knew how to knit except my mother and we decided to make one hat for each year."
Together the pair have made about 120 hats since starting in November.
As is customary when turning 100, the Queen sent her regards to Maud in a birthday card.
"When she opened the Queen's letter she was beaming from ear-to-ear," said St Anne's Debbie Soper.