Seaton Valley locality lies in the South East of Northumberland, bordering the Metropolitan Borough of Tyne & Wear, and has a population of 15,422(1). In terms of area, it measures 28.4 km² (the largest of the 10 localities in South East Northumberland), and has a population density of 540 people per km².
Seaton Valley locality includes the villages of Holywell, New Hartley. Seaton Delaval, Seaton Sluice and Seghill.