 He was also a Justice of the Peace, a Deputy Lieutenant, and High Sheriff of Cambridgeshire and Huntingdonshire in 1859.In 1872, John Dunn Gardner was the sixth largest landowner in the county of Cambridge, ranking immediately after the Earl of Hardwicke, the Duke of Bedford, John Walbanke Childers MP, the Duke of Rutland, and William Hall.He was the second largest landowner to be resident principally in Cambridgeshire, and owned , or about 0.7% of all land in that county.