Willem Coertzen (born 30 December 1982, in Nigel) is a retired South African track and field athlete who competed in the decathlon.

He began taking part in decathlon competitions in 2007 for Shaftesbury Barnet Harriers in the United Kingdom, where he won the South of England Combined Events Championship in Bedford with a total of 7245 points.

The following year he returned to his native South Africa to win his first national decathlon title, then recorded a personal best of 7721 points in Réduit.

[3] The following May he completed two decathlons: he set a new South African record in the event with a score of 7907 points for third place at the Multistars meeting in Desenzano del Garda.

[1] He edged out Olympic medallist Dmitriy Karpov at the TNT - Fortuna Meeting in June 2011, taking third place with a score of 8094 points (which included personal bests in the discus throw, shot put and 1500 metres).