Thorndon Park Reserve is a public park in the Adelaide suburb of Paradise, South Australia. It was originally the site of the Thorndon Park reservoir, which was completed in 1860. The reserve became accessible to the public for recreational use in 1986. It was redesigned in the 2000s and as of 2015 improvement works are ongoing.

The reserve has picnic areas, barbecues, play equipment for children, large grassy areas, wheelchair-friendly walking paths, an amphitheatre, waterways and a terraced series of ponds and wetlands which support diverse native flora and fauna. In 2014, the prospect of establishing a community orchard within the Thorndon Park Reserve was considered. Dogs are not permitted in the park.

Thorndon Park Reservoir
Thorndon Park Reservoir, 1899
Coordinates	34°52′28″S 138°41′18″E / 34.87444°S 138.68833°E / -34.87444; 138.68833
Status	Drained and converted to a park
Construction began	1857
Opening date	1860
Demolition date	1986
Dam and spillways
Type of dam	earth
Height	42 feet (13 m)
Width (crest)	5 feet (1.5 m)
Width (base)	10 feet (3.0 m)
Reservoir
Total capacity	142,000,000 imperial gallons (650 Ml)
Surface area	26.5 acres (10.7 ha)
Maximum water depth	40 feet (12 m)

The Thorndon Park reservoir was the first reservoir built to supply the township of Adelaide. It was under construction between 1857 and 1859 and was completed in 1860. At full capacity, the reservoir held 142,000,000 imperial gallons (650 Ml) of water.

In 1950 the tiny African freshwater jellyfish Craspedacusta sowerbii was found in the reservoir.

• List of Adelaide parks and gardens
• List of reservoirs and dams in Australia