For Nottinghamshire, on often overgrassed Trent Bridge pitches, he gained some analyses that are remarkable in an era of covered pitches, notably his eight for 22 against Surrey in 1984. He represented Nottinghamshire between 1978 and 1987, but played only three full seasons due to injuries and Test calls. However, his bowling figures for those three seasons were quite remarkable:
1981: 4252 balls, 231 maidens, 1564 runs, 105 wickets for 14.89 each.
1984: 4634 balls, 248 maidens, 1645 runs, 117 wickets for 14.05 each.
1987: 3408 balls, 186 maidens, 1154 runs, 97 wickets for 11.89 each (the lowest average since 1969).
In those three seasons he was voted the PCA Player of the Year by his peers of the Professional Cricketers' Association (PCA). He won The Cricket Society Wetherall Award for the Leading All-Rounder in English First-Class Cricket in 1982, 1984, 1986 and 1987.
In the 1984 county season, Hadlee completed a feat rare in the modern age by doing the county 'double' – scoring 1000 runs and taking 100 wickets in the same season. Hadlee, and his immediate successor at Nottinghamshire Franklyn Stephenson, are the only two players to achieve this feat in English county cricket since the number of county games per season was reduced in 1969. The runs component of the double included Hadlee's highest first class score, 210* in a victory over Middlesex at Lord's. In 1987, his swan song, he narrowly missed the double as Nottinghamshire won the County Championship as they had in 1981. Hadlee's contribution with ball and bat to both and their other triumphs was immense. They next won the championship in 2005 with fellow Kiwi Stephen Fleming in charge.