The prince and his wife, the former Kate Middleton, planned to just have a few close friends over for a private dinner at their home in north Wales.
With his milestone birthday, Prince William is set to receive an esimated $15 million under the terms of the will of his late mother, Princess Diana. The exact amount is not known because the current value of the trust set up by his mother has not been made public.
William, who is second in line for the throne behind his father, Prince Charles, has been pursuing a military career as a search-and-rescue helicopter pilot.
The Associated Press contributed to this report.