For many years, previous to World War I, the house had been the residence of the widow of the 4th Duke of Northumberland, Eleanor, Duchess of Northumberland. The Duchess lived for 40 years at the house until her own death in 1911. She became so attached to the estate that she chose to be buried in the village church, which she had rebuilt by Salvin, rather than the Northumberland vault in Westminster Abbey. During her occupancy of the house the gardens were expanded and developed, these included an Italian garden also designed by Salvin. During this period the gardens were renowned for their glass houses producing, what at the time were considered, rare and exotic fruitss such as bananas, peaches, grapes, figs and nectarines, some varieties such as the "Stanwick nectarine" were propagated and bred on the estate.
The interior of the house contained many fine 18th century features, before the demolition some of the decorations and motifs were removed. Three of the rooms were removed completely and are today believed to be those re-assembled in the Minneapolis Institute of Arts. Comparisons with the extant photographs of the house interiors cast doubt upon this, and the links are doubtful; the director of the institute visited Alnwick in the thirties to check on the provenance - no record seem to exist of his ultimate findings. A firm called Robersons in London were in this business. It seems possible that since there were 22 rooms from different houses being traded, of which only three were offered from Stanwick, there may have been an error. Museums in Roslyn, NY, and Toronto, as well as the collection of William Randolph Hearst are also alleged to have Stanwick rooms.