James Simpson FRS FRSA (1799–1869) was a British civil engineer.

James succeeded his father in both this post and that of engineer of the Lambeth Waterworks Company.

It was under Simpson's instruction that the Chelsea Waterworks became the first in the country to install a slow sand filtration system to purify the water they were drawing from the River Thames.

[2] This filter consisted of successive beds of loose brick, gravel and sand to remove solids from the water.

[3] He also designed waterworks at Windsor Castle and Bristol as well as The Wooden Pier at Southend-on-Sea.