Lourd and her fiancé, Austen Rydell, have welcomed a son, Kingston Fisher Lord Rydell.
Lourd had not previously disclosed the news that she and Rydell were expecting.
"Introducing Kingston Fisher Lourd Rydell," the caption read with heart and crown emojis.
In June, Rydell shared a series of photos and a video of the couple to announce their engagement.
Rydell is an actor and a producer, while Lourd is well-known for her roles in "American Horror Story" and "Star Wars: Episode VIII - The Last Jedi" where she starred alongside her mother.