The 32-year-old is due to marry in September in an intimate ceremony in London and wants to celebrate with their friends in the UK and US, reported Digital Spy.
"Dawn has her UK celeb mates coming to the first wedding, like Caroline Flack, but they'd love an LA bash too," a source said.
O'Dowd proposed to Porter last December, and has recently revealed that his fiance has turned into a very controlled wedding planner in the process of organizing their special day.
