Juan Thornhill (born October 19, 1995) is an American professional football safety. He played college football for the Virginia Cavaliers and was selected by the Kansas City Chiefs in the second round of the 2019 NFL draft. He has also played for the Cleveland Browns and Pittsburgh Steelers.

Thornhill attended Altavista High School in Altavista, Virginia. He played safety and quarterback in high school. He committed to the University of Virginia to play college football. Thornhill also played basketball in high school.

Thornhill played at Virginia from 2015 to 2018. Thornhill played cornerback and safety at Virginia, where he graduated in December 2018 with a degree in anthropology. During his career, he had 208 tackles, 13 interceptions and 1.5 sack.

Scouts Inc. ranked Thornhill as the sixth best safety in the draft (60th overall). Pro Football Focus also ranked him sixth best amongst his position. NFL.com analyst and former NFL executive Gil Brandt ranked Thornhill as the third best safety in that year's draft (53rd overall). Sports Illustrated ranked him seventh best among safeties (83rd overall).

The Kansas City Chiefs selected Thornhill in the second round (63rd overall) of the 2019 NFL draft. Thornhill was the sixth safety drafted in 2019. The Chiefs originally acquired the second-round pick (63rd overall) during a trade for cornerback Marcus Peters with the Los Angeles Rams in 2018.

On May 14, 2019, the Kansas City Chiefs signed Thornhill to a four–year, $4.64 million contract that includes $1.79 million guaranteed and an initial signing bonus of $1.37 million. Throughout training camp, Thornhill competed to be the starting free safety against veteran Daniel Sorensen. The role was vacant after the Chiefs released Eric Berry and following the departure of Eric Murray in free agency. Head coach Andy Reid named Thornhill the backup free safety, behind Daniel Sorensen, to begin the regular season.

During pre-game warmups, head coach Andy Reid unexpectedly chose to start Thornhill at free safety immediately after kickoff. He made his first career start in his professional regular season debut in the Kansas City Chiefs' season-opener at the Jacksonville Jaguars and recorded a season-high eight combined tackles (five solo) during a 40–26 victory. He was named the starting free safety moving forward and was paired with starting strong safety Tyrann Mathieu. On October 13, 2019, Thornhill made four solo tackles, a pass deflection, and had his first career interception off a pass thrown by Deshaun Watson to wide receiver Keke Coutee during a 31–24 loss against the Houston Texans. On December 1, 2019, he recorded four combined tackles (three solo), broke up a pass, and intercepted a pass by Derek Carr to wide receiver Tyrell Williams and returned it for 46–yards as the Chiefs routed the Oakland Raiders 40–9. On December 29, 2019, Thornhill tore his left ACL during a 31–21 victory against the Los Angeles Chargers. He finished his rookie campaign with a total of 58 combined tackles (42 solo), five pass deflections, three interceptions, and one touchdown while starting all 16 games. He was named to the PFWA All-Rookie Team.

The Kansas City Chiefs finished the 2019 NFL season first in the AFC West with a 12–4 record, clinching a playoff berth and first round bye. They went on to defeat the Houston Texans and defeated the Tennessee Titans 35–24 in the AFC Championship Game. On February 2, 2020, the Kansas City Chiefs defeated the San Francisco 49ers 31–20 to win Super Bowl LIV. This earned Thornhill his first Super Bowl ring.