Frank Willenborg (born 10 February 1979) is a German football referee who is based in Osnabrück.

He referees for SV Gehlenberg of the Lower Saxony Football Association.

Willenborg, who referees for SV Gehlenberg, has been a DFB official since 2004.

In the summer of 2016, Willenborg was one of four referees promoted to officiate in the Bundesliga.

He also temporarily worked at the secondary school "Hauptschule Dinklage" as a substitute teacher for German and sport.