"Welcome to the world, @AtlasNickson," Jessica captioned a family photo featuring Cody and the baby.
Atlas was born on Saturday, July 16, weighing six pounds and one ounce.
Cody, 36, uploaded the same post, and then several hours later, he posted an Instagram slideshow of images from the hospital -- including a video of Cody holding his baby daughter in his arms and rocking her as they watched TV together.
"Me and my new baby girl, Atlas," he wrote alongside the pictures.
The couple told Us Weekly in a statement that they've always "wanted a big family."
"On Saturday morning, we were fortunate enough to add another healthy baby girl to that dream," Jessica and Cody gushed. "Atlas Ruby Nickson, welcome to the big world, baby. We're so excited to see what you make of this life God has gifted you!"
Jessica went into labor earlier than expected at 36 weeks pregnant, and Atlas arrived at 10:15AM CT.
On June 18, Jessica posted a photo that read, "IT'S A GIRL," confirming the baby's sex.
Jessica captioned it, "In case you missed it. We're adding to our girl gang! In just a few weeks we'll be bringing Atlas Ruby Nickson home to forever change our family and we can't wait."
Jessica revealed her baby's name all the way back in May.
"Nickson Addition 08.2022 @babynickson," the couple captioned an Instagram video on their respective accounts showing footage of the couple, their two young girls, and sonogram images of their baby on the way.
"A lot of you have already guessed it and it's nice to not have to hide it anymore. We prayed for you & now we can't wait to meet you."
The video was set to "You Are My Sunshine," and one sweet image featured Cody and Jessica embracing as they cradled her noticeable baby bump.
Jessica and Cody are already parents of daughters Maverick, 3, and Carter York, who turns two years old this October.
Cody also has a daughter Paisley from a previous relationship.
In January, Cody and Jessica closed on a bigger home in Dallas, TX.
Jessica revealed on Instagram at the time, "When we got married we made a 10 year plan to build a home. Never did we imagine we would do it in 3! The opportunity was just perfect and we couldn't turn down the chance."
"We started this project last January and a full calendar year later, here we are, keys in hand and a lot more work ahead. But this is the exciting part. Unpacking and making our new house a home in this next chapter of life."
Back in December 2020, just two months after Jessica gave birth to the couple's second child, Cody said he couldn't wait to get his wife pregnant again and was really looking forward to having a third baby.
"What are you most excited for in 2021?" a fan asked Cody when the reality TV star conducted a Q&A session on his Instagram Story at the time.
"Getting my wife pregnant again," Cody replied, before adding, "(I'll tag her @thejessicanickson so she can slap me later. Ha)."
In reply to Cody's post, Jessica wrote on her own Instagram Story, "If this happens, it'll be LATE 2021 lol!"
Jessica did not debut her first baby bump until she was 22 weeks along with Maverick in order to avoid haters and trolls, but Jessica was much more confident and open with fans during her second pregnancy.
"FINALLY! As you guys know, Cody and I have been wanting to have all our kids pretty close in age so we were determined to get pregnant this year... Maverick is going to be a big sister!" Jessica wrote at the time.
"I'm not really sure if she fully understands that yet but no matter what, she's always going to be my baby."
The couple then unveiled the sex of Baby No. 2 on May 12, 2020 by posting a gender-reveal video to Jessica and Cody's YouTube channel.
"I had no idea that one day I would be on [Big Brother], nor that it would change the course of my life forever. I met the love of my life, Jessica. I don't say that lightly," Cody wrote on Instagram in October 2021.
"Since the day we met, we've spent almost every waking and sleeping moment together. We are inseparable. We would go on to win the Amazing Race together as a team, and this would give us the money to buy our house, grow our businesses, get married, and start our family."