The couple welcomed a daughter - Della Rose Joel - who weighed 7 lbs 6.5 oz according to PEOPLE.
Although this is Roderick's first child, Joel, already has one daughter Alex Ray Joel, 29, with former wife Christie Brinkley.
Billy Joel and wife, Alex Roderick
The 66-year-old singer, most known for his song "Piano Man" married his fourth wife, Alexis Roderick, 29, on 4 July 2015.
The couple announced back in April 2015 that they were expecting their first child together.
In June, when asked how he felt about becoming a dad for the second time, Joel told UPI: "[It's] Pretty wild, huh? I've still got the mojo. I'm excited!
"I'm gonna spend a lot of time with this kid. I'm probably going to be able to spend more time with this kid than most people are able to spend with their children, because I don't have a regular job.
"I could be a stay-at-home dad for as long as I can stay alive."