The baby, which was born yesterday, is the couple's first child together.
A representative for Kimmel confirmed the news, saying the baby's name is Jane, and mom is "doing great."
Kimmel also tweeted the news: "Congratulations to my beautiful and very tough wife @mollymcnearney on delivering our baby girl this morning.
"Thanks for all your kind baby wishes-turns out, not ALL tweets are mean!"
Kimmel is also father to son Kevin and daughter Katherine from his first marriage to Gina Maddy.