Jonah Frantzich was born in Stillwater, Minnesota to Carrie and Timothy Frantzich. His parents used to come up to the small town called "Grand Marais" every summer, one year they couldn't because he was born when their trip was scheduled, which is where part of his namesake derived from. He has three siblings: Zebulon Frantzich (born December 26, 1991), Esther Frantzich (born March 31, 2000), and Svea Frantzich (born March 21, 2007).
Everyone in his family is musically talented, and sang wherever they could, including at fairs, and churches. They once sang Jason Mraz's "I'm Yours" at a corner outside a bakery.
Jonah taught himself to play instruments and to sing. When he was in sixth grade he did his first talent show which was a piano cover of John Lennon's "Imagine".
Jonah used the platform YouNow in 2014, and at the end of summer gained 10k followers, and was able to do social media tours through this. Halfway in his tenth grade he dropped out of school to fully pursue his musical career. His first live performance was at DigiFest in front of 7000 people. He also met his future band mates Corbyn, Jack, and Zach through touring. On July 7, 2015, his first released single "I Meant It" was dropped along with its music video in August the same year. In March 2016 his single "War Paint" was released and served as the lead track for his first debut EP When the Daylight's Gone in April 2016. He also went on his own solo tour.
He dated Dani Cimorelli, the youngest member of the group "Cimorelli" (She left in Jan 2020 and started her own YouTube channel called Dani Calleiro), from August-October 2014. Dani made a video about the relationship in 2015, as part of the Cimorelli Storytime series, without taking his name, and made another video on her own channel in 2020, where she did drop his name, as many people already knew about the relationship by then. Jonah mentioned the relationship in their book too, which was released in 2018. After the breakup, the two maintained their distance. The two respect each other but prefer not to talk about each other. Contrary to popular belief, 'Perfect' by Why Don't We is not about Dani, as Jonah didn't consider the relationship as 'serious'. There is also no evidence in their relationship that matches up with the lyrics of the song. However, the Cimorelli song, 'Before October's Gone' off the 'Up At Night' album is based on their relationship. Jonah even promoted the album on Twitter in 2016, proving that there is no bad blood between them. Promotion of the Cimorelli Album, 'Up At Night'.
He dated Alyssa sometime near the end of 2014-2015. They released a cover of One Direction's "Little Things" together. There was some controversy over the relationship as she was three years older than him. Despite their breakup, they remained good friends.
He and Tate met when filming the music video "Trust Fund Baby". Their relationship is kept private, but fans speculate that they have been dating since 2018.