2022: Johnsen redshirted for the Cowboys during his first season with the program.

High School: Rex Johnsen is rated as a three-star recruit by 247 Sports. 247 Sports ranks Johnsen as the No. 15 overall recruit in the state of Iowa this season. Johnsen was named to the 2021 Des Moines Register All-State Class A First Team as an offensive lineman. He also was named First Team All-State Class A as an offensive lineman by the Iowa Print Sports Writers Association. Johnsen played offensive tackle and defensive end for Logan-Magnolia High. His senior season, Johnsen was credited with 34 tackles, including 22 solo tackles, 11.0 tackles for loss and 5.5 sacks. His junior season, he made 46 tackles, with 28 of them being solo tackles. He added 9.5 TFLs and 4.0 sacks as a junior. Johnsen helped lead Logan-Magnolia to a 9-2 record his senior season and the Quarterfinals of the 2021 Class A State Playoffs. Johnsen also competes for his high school wrestling team. His junior season, he placed second at the Iowa Class 1A State Wrestling Championships at 285 pounds, while his Logan-Magnolia High team finished third in the team standings. Johnsen played for head football coach Matt Straight. Johnsen was recruited by Iowa State, Nebraska and North Dakota State. 2e:{"college":"North Dakota","college_logo_url":"https://assets.nextgenprospect.com/42c541865adbd7ed1f6b615878c4c6f0?X-Amz-Expires=7200&x-amz-acl=public-read&X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=FRWUX7KZFXNEMMV55BPI%2F20250406%2Fnyc3%2Fs3%2Faws4_request&X-Amz-Date=20250406T194140Z&X-Amz-SignedHeaders=host&X-Amz-Signature=c256afdf27a334f38e6a71f2e11096fe84ce11ba4d848a814fe0b0d2764821d6"} 2f:{"college":"North Dakota State","college_logo_url":"https://assets.nextgenprospect.com/7cde7ea7a5f0d7899fa2714f9cda8c1d?X-Amz-Expires=7200&x-amz-acl=public-read&X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=FRWUX7KZFXNEMMV