Haddon Corner is a heritage-listed site in Tanbar, Shire of Barcoo, Queensland, Australia. It is in outback Channel Country at South-West Queensland, on the border corner with South Australia. It was added to the Queensland Heritage Register on 9 November 2012.

It was first surveyed by Augustus Poeppel in 1880. Haddon Corner lies at the intersection of the 26th parallel south circle of latitude and the 141st meridian.

Karuwali (also known as Garuwali, Dieri) is a language of far western Queensland. The Karuwali language region includes the landscape within the local government boundaries of the Diamantina Shire Council, including the localities of Betoota and Haddon Corner.

Haddon Corner, marked in 1880 during the official survey of the western section of the border between Queensland and South Australia undertaken in 1879–1880, defines the north-eastern corner between Queensland and South Australia. Its marking was a surveying feat of its time.

Letters patent issued by Queen Victoria in June 1859 separated the new Colony of Queensland from New South Wales (NSW). They described Queensland's border as the watershed from Point Danger (28°8"S) west to the Dumaresq River; the Dumaresq, Macintyre and Barwon Rivers to latitude 29 degrees South; and along latitude 29 degrees South to the 141st meridian of East longitude, which was the eastern boundary of South Australia.

Although legal opinion advised that the 141st meridian was the western boundary of Queensland, Surveyor-General Augustus Charles Gregory believed otherwise. In a memorandum of 28 September 1860 he wrote "the western boundary ... appears to be the 141st meridian; but it is probable that it was not described in the Letters Patent erecting the Colony, with greater distinctness, expressly with a view to a future adjustment, when more certain information should have been collected as to the natural features of the country... It is now submitted that the 141st meridian passes through the tract of country known as the "Plains of Promise" and that the Eastern shore [of the Gulf of Carpentaria] possesses no harbours. It would therefore be desirable to adopt the 138th meridian as the boundary; as that line would pass through a barren tract of country, and bring "Investigator's Road' [an anchorage] within the limits of Queensland.'

Furthermore, expeditions in 1861-1862 funded by the South Australian, Victorian and Queensland governments to rescue the missing explorers Burke and Wills, who had failed to return from a journey from Cooper Creek to the Gulf of Carpentaria, led to the exploration of an enormous area of the inland and were predicted to stimulate interest in this previously unknown tract of land beyond Queensland's western boundary. Writing to the Secretary of State for the Colonies on 5 September 1861, the Queensland Governor George Bowen indicated his colony's willingness to protect any settlers so attracted, provided that the western boundary could be extended to include the Gulf. The proposal was accepted on condition that the additional territory could be reclaimed later should another colony be formed in northern Australia.

In response, a despatch dated 14 December 1861 from the Secretary of State for the Colonies advised that the proposed annexation to the 138th Meridian of longitude should be revoked under Act 24 and 25 Victoria, c.44. This immediately provoked a despatch from Sir George Bowen, dated 18 January 1862, stating that Queensland had taken provisional control of this area. Subsequently, on 12 April 1862 Letters Patent were issued describing the accession of "so much of our Colony of New South Wales as lies to the northward of the 26th parallel of south latitude and between the 141st and 138th meridian of east longitude...". Thereby two more corners in Queensland's western boundary were created and the colony acquired part of the Barkly Tableland and the area which later became the Mount Isa mineral field. A revised definition of the extent of Queensland was subsequently proclaimed on 23 June 1862.