Cornelsen was a three-year starter and four-year letter winner at quarterback for the Lions. He was the first quarterback in NCAA Division II history to pass for 4,000 yards and rush for 2,000 yards in a career.

He was an Academic All-Conference selection in both 1997-98 and was a Harlon Hill Regional Finalist in 1997. He finished his career fourth all-time on the total offense list with 6,671 yards. He had the highest passing efficiency mark in MSSU history in 1996 when he put up a mark of 162.5. He completed 102 passes in 189 attempts for 1,625 yards and ten touchdowns. He also ranks seventh all-time in career rushing yards (second amongst quarterbacks) with 2,273 yards and ranks fourth in career scoring (210). He is fifth in both passing yards (5,334) and completions (261).

Cornelsen started his coaching career at Northeast Oklahoma A&M, and served stints at Northwest Missouri, Oklahoma State, Illinois State, Northeastern State and has served as a quarterbacks coach at the University of Memphis for the past three seasons. In 2013, Cornelsen coached freshman Paxton Lynch to become just the second Tiger to throw for over 2,000 yards in his rookie campaign. It was also just the tenth 2,000 yard passing campaign in Memphis program history and Lynch ranked in the top ten in single-season pass attempts, completions and completion percentage.

Cornelsen graduated from Southern in 2000 with a degree in physical education and he and his wife Jaimi were married in 2011.