The Thirlmere Lakes National Park is a protected national park that is located in the Macarthur region of New South Wales, in eastern Australia. The 629-hectare (1,550-acre) national park is situated approximately 70 kilometres (43 mi) southwest of the Sydney central business district, and just to the west of Thirlmere. It was gazetted in 1972 as Thirlmere Lakes State Park, before being subsequently reclassified as a national park.

Macarthur is a region in the south-west part of the Greater Sydney area, in the state of New South Wales, Australia. The region includes the local government areas of the City of Campbelltown, Camden Council, and Wollondilly Shire. It covers an area of 3,067 square kilometres and has a population of close to 310,000 residents. The region geographically forms the foothills between the Blue Mountains and Southern Highlands regions.