Poeppel Corner Survey Marker, Survey marker at the Queensland–Northern Territory–South Australia border, Australia

The Poeppel Corner Survey Marker is a boundary stone marking the exact meeting point of Queensland, Northern Territory, and South Australia. It sits in a remote location within the Simpson Desert near Lake Poeppel.

Queensland's western border was extended to the 138th meridian by Letters Patent of 12 April 1862, creating this corner. Pastoralists' boundary disputes, including James McLeod's 1877 request, pushed for a survey. Surveyors Augustus Poeppel and Lawrence Wells fixed the marker in 1879–1880; the mapped border lies several hundred metres from the nominal 26°S 138°E point.

The corner takes its name from Augustus Poeppel, the surveyor who fixed the 26th parallel and 138th meridian here in 1879–1880. Pastoralists had pressed for the border survey since the 1870s, after James McLeod of Cullamurra disputed station boundaries with John Conrick of Nappa Merrie. The marker was added to the Queensland Heritage Register on 9 November 2012.

The marker lies in the Simpson Desert, about 300 km west of Haddon Corner and 450 km north-west of Cameron Corner, with no formed road access; only a four-wheel-drive convoy with water and fuel carried for the full distance can reach it. The Queensland side falls in Munga-Thirri National Park, the South Australian side in the Munga-Thirri—Simpson Desert Conservation Park, so check park access rules before setting out. The mapped border sits several hundred metres from the nominal 26°S 138°E point, so navigate to the marker itself, not the coordinates.

The marker received recognition on the Queensland Heritage Register in 2012 for its role in establishing precise geographical boundaries. It stands as evidence of early surveying methods accomplished without modern technology.