Thomas Westby (1641-1700) was the head of the Westbys, a family that came from the village of Westby in Yorkshire and was established at Mowbreck, near Kirkham, from about 1300, also owning Burn Hall, near Thornton. They took their name from the Yorkshire village of Westby, not the one in the Fylde, which was part of the estate of their neighbours, the Cliftons. The Westbys and the Cliftons were the leading gentry Catholic families in the Fylde in the 17th century. In 1669 Mowbreck was listed as the site of a Catholic conventicle. Thomas, who was living at Burn Hall, succeeded his uncle, John Westby of Mowbreck, who had died childless in 1662. Thomas continued to live at Burn Hall, while his aunt, John’s wife, Dorothy, stayed on at Mowbreck Hall. Thomas was married to Thomas Clifton‘s sister, Bridget, and had three sons John, Thomas and Robert. 
Both Westby and Clifton were accused of treason at the Manchester Jacobite trials in 1694. At the trial it was claimed that in June 1689 Thomas Westby was commissioned colonel of a regiment of dragoons in forces being raised to support an attempt to reinstate James II. Other Westbys were also allegedly offered commissions. The evidence was discounted at the trial, and Westby and his co-defefendants were acquitted.