The comedy actor, who has starred in films including Napoleon Dynamite, Blades of Glory and School for Scoundrels, shared the happy news on his Instagram account on Father's Day, telling his 20,000 followers, 'Appropriate day to announce this. Gonna be a dad again! Kids had mixed reactions. Kidding, they're all excited! Due date's Christmas Eve though. Haha, sucker...'
Jon, 38, also confirmed that the couple already know the gender of their new arrival by including an 'It's a Girl!' announcement in the accompanying picture.
Fans were quick to celebrate the news, with one commenting 'So excited for you! Hooray!' and another adding 'Oh my gosh!!! Congrats you guys!! What happy news!!'
Jon and his wife Kirsten met when they were both were students at Brigham Young University, and got married in 2002.
They are already parents to three children; daughter Evan, 9, and sons Philip, 7, and Timothy, 2.
Speaking to LDS Living in 2012, Jon said that his fame hadn't really had an impact on his growing family.
'My kids really have no idea what’s going on yet, so they’re not bothered by it,' he stated at the time. 'In fact, they like jumping in the middle of a fan picture. I guess when I'm at Disneyland, I get approached a lot and that keeps my kids from getting on the Dumbo ride all the sooner, so I suppose that affects my family experience, right?'
However, he added that becoming a father has had an impact on the way he considers prospective roles.
'Being a father is a just a small part of everything that influences my decisions regarding my roles. Being a son, a husband, a father, a brother, a church member, a Scoutmaster, etc… everything I am influences my choices. Every job I take, I think about how it will affect my abilities to fulfil the duties required by each of these roles in my life.'