John Rounsevell (ca.1836 – 15 May 1902) was a pastoralist and politician in the British colony of South Australia. His brother William Benjamin "Ben" Rounsevell was also a South Australian politician.
John Rounsevell was born in Landunna, Cornwall and came out to South Australia with his parents William and Grace Rounsevell in the City of Adelaide arriving on 6 July 1839. He was educated at St. Peter's College, then started working for his father's livery stable and mail coach business, becoming a partner with responsibility for operations north of Kapunda. He became an expert horseman and a foremost exponent of the whip.
He retired from "the road" when the company was sold to Cobb and Co.. He managed his father's property Corryton Park (which he later inherited) near Mount Crawford and turned his attention to filling Government contracts. He supplied sleepers for railway work and supervised construction of the 500-mile (800 km) section of the Adelaide to Darwin telegraph line north from Port Augusta, and supplied a great number of its telegraph poles as well as large numbers of horses, bullocks and camels for the project.
In 1864 he took up pastoral country in the vicinity of the Warburton Range and lying to the north-east and south-east of it, and erected the trig point on Rounsevell Hill, to the north-west. He also named Gibraltar, the large granite outcrop in the district, and Sturt's Rock, named for the number of Sturt peas in the neighbourhood.
He turned his attention to sheepfarming, at Corryton Park, successfully breeding stud sheep, while his wool clips had a good reputation both in South Australia and in London.
In 1865 John Rounsevell was elected as a member of the South Australian House of Assembly for the district of Light, but he retired two years later.
Subsequently he sat in the House of Assembly for the district of Gumeracha.