Nicholas Saunderson, 1st Viscount Castleton (1562–1631) was an English landowner and politician who sat in the House of Commons in 1593 and 1625. Saunderson was the eldest son of Robert Saunderson of Saxby and Fillingham and his second wife Catherine Grantham, daughter of Vincent Grantham of St Katherine's, Lincoln. He was educated at Oxford University, being awarded BA in 1579, and also entered Lincoln's Inn in 1579. He succeeded to the estates of Saxby and Fillingham at the age of 21 on the death of his father and became one of the leading landowners of Lincolnshire. By 1569 he was commissioner for sewers for Lincolnshire. He was J.P. for Lindsey Lincolnshire from 1591 and JP for Nottinghamshire from about 1592. He was High Sheriff of Lincolnshire from 1592 to 1593.