Aniston, 44, chatted with her female colleagues whereas the birthday boy, who received gifts from Cartier and Barney's, spent a majority of the night with Shepard and Jimmy Kimmel, reported Us magazine.
"Several of Justin's friends spent the afternoon at the house hanging out by the pool with him and celebrating his birthday.
"It was a relaxed afternoon and they were all in the cabana area having drinks and listening to music like Kanye West and The Kinks," a source said.
The birthday celebration also marked the one-year anniversary of the couple's engagement.