The 48-year-old actor invited a slew of A-listers for a weekend getaway at Cavallo Point Lodge in Sausalito, Calif., north of San Francisco.
Sources say the family-friendly celebration, held in the hotel's ballroom Saturday night, featured dinner, dancing, games, and that perennial party favorite, the photo booth. White roses and purple lights decorated the space, along with plenty of photos of Susan Downey, and the night capped off with a round of fireworks over the bay.
The Downeys' 21-month-old son Exton was there for the fun, and Gwenyth Paltrow and Reese Witherspoon were both there, along with their kids. Other partygoers included Justin Theroux, Jason Bateman, Jon Favreau, Maya Rudolph and Gavin Rossdale.
On Sunday morning, guests enjoyed brunch from the Hapa SF and Bacon Bacon food trucks. And before the weekend was over, there was even more bacon: Susan Downey was treated to a round of "Happy Birthday" and a cake made with maple bacon, chocolate bacon, bacon bits, bacon jam and vanilla cake.
Sounds like a delicious -- and memorable -- 40th!
Notable deaths of 2014 [PHOTOS]