Following the Clough 's resignation in 1973 , his successor Dave Mackay guided Derby County to another league title in 1975 , but this remains to date the club 's last major trophy ; relegation followed in 1980 and top flight status was not regained until 1987 , since then Derby have spent a total of 11 seasons ( 1987-1991 , 1996-2002 , 2007-2008 ) in the top flight .
Following the Clough 's resignation in 1973 , his successor guided County to another league title in 1975 , but this is the club 's last major trophy to date ; relegation followed in 1980 and top flight status was not regained until 1987 , since when Derby have spent a total of 10 seasons ( across two spells ) in the top flight .