Peter Ainsworth DL JP (24 November 1790 – 18 January 1870) was a British landowner and operator of an important bleach works.
Leaving the family business to a brother, he went into politics as a Whig, and was one of the two Members of Parliament for Bolton from 1834 to 1847, before returning to the life of a country gentleman.
[1] On his father's death Ainsworth inherited the Smithills Hall estate and a large shareholding in the bleach works, but he became an inactive partner in it, preferring the life of a country gentleman.
In 1834 he was elected to the House of Commons as a Whig member of parliament for Bolton, and he held the seat until 1847, serving alongside William Bolling and John Bowring.
He lived mostly at Smithills Hall, part of which he rebuilt, while his younger brother, John Horrocks Ainsworth (1800–65), carried on the family business.