The actress, 29, and her husband Ryan Reynolds, 39, have not yet revealed the baby’s name or sex.
A source told Us Weekly Lively’s sister Robyn and her friend Taylor Swift visited her in hospital to meet the new arrival.
Lively and Reynold’s second child joins big sister, James, who is 22 months.
Lively and Reynolds began dating in 2010, then tied the knot in a private ceremony two years later.
They welcomed their first child in January 2015. and revealed they were expecting their second child together in APril 2016.