Thomas Penson, or Thomas Penson the younger was the county surveyor of Denbighshire and Montgomeryshire, and an innovative architect and designer of a number of masonry arch bridges over the River Severn and elsewhere.

Thomas Mainwaring Penson (1818–1864) was an English surveyor and architect. His father and grandfather, who were both named Thomas Penson, were also surveyors and architects. His grandfather Thomas Penson worked from an office in Wrexham, North Wales, and was responsible for the design of bridges, roads, gaols and buildings in North Wales. His son Thomas Penson (1790–1859) was county surveyor to a number of Welsh counties and also designed bridges. He later moved to Oswestry, Shropshire where he established an architectural practice. Thomas Mainwaring Penson was born in Oswestry, and was educated at Oswestry School. His elder brother was Richard Kyrke Penson who became a partner in the Oswestry practice in 1854, before developing an extensive architectural practice of his own, mainly in South Wales. Thomas Mainwaring Penson trained in his father's practice. Thomas Mainwaring initially designed buildings in the area of the practice, including stations for the Shrewsbury and Chester Railway.