Speaking to Hello! magazine, the campaigner revealed she has spent most of her time helping out with charity projects in the US.
Ms Mills, who completed her much publicised divorce from Paul McCartney in May, said she had donated $1 million (£565,000) worth of vegan food to a poor neighbourhood in New York.
"A lot of [the money] has already gone to charity, and I kept some to invest in projects and causes that will make the world a better place," she told Hello!.
The model has moved permanently to the US with four-year-old daughter Beatrice.
A recent government survey revealed that less than half the adult population in England and Wales are now married.
Figures published by the Office for National Statistics earlier this week showed that 21,535,000 adults were married - just 49.5 per cent of the population over 16.
