1990–91 Rugby Union County Championship

The 1990–91 ADT Security Systems Rugby Union County Championship was the 91st edition of England's County Championship rugby union club competition.

Cornwall won their second title (but first since 1908) after defeating Yorkshire in the final. The significant Cornwall following resulted in a new record attendance of 56,000 at Twickenham Stadium. The final signified the greatest match in the history of the competition.