Geelong (/dʒɪˈlɒŋ/ jih-LONG; Wathawurrung: Djilang/Djalang) is a port city in Victoria, Australia, located at the eastern end of Corio Bay (the smaller western portion of Port Phillip Bay) and the left bank of Barwon River, about 75 km (47 mi) southwest of Melbourne. With an estimated population of 282,809 in 2023, Geelong is the second-largest city in the state of Victoria. It is the administrative centre for the City of Greater Geelong municipality, which is Port Phillip's only regional metropolitan area, and covers all the urban, rural and coastal reserves around the city including the entire Bellarine Peninsula and running from the plains of Lara in the north to the rolling hills of Waurn Ponds to the south, with Corio Bay to the east and the Barrabool Hills to the west.

The traditional owners of the land on which Geelong sits are the Wadawurrung (also known as Wathaurong) Aboriginal people of the Kulin nation. The modern name of Geelong, first recorded in 1827, was derived from the local Wadawurrung name for the region, Djilang, thought to mean "land", "cliffs" or "tongue of land or peninsula". The area was first surveyed by the European settlers in 1838, three weeks after Melbourne. During the 1850s Victorian gold rush, Geelong experienced a brief boom as the main port to the goldfields of central Victoria. The town then diversified into manufacturing, and during the 1860s became one of the largest manufacturing centres in Australia with its wool mills, ropeworks, and paper mills. During the city's early years, inhabitants of Geelong were often called Geelongites or Pivotonians, derived from the city's nickname of "The Pivot", referring to the city's role as a shipping and rail hub for Ballarat and the Western District.

Geelong was proclaimed a city in 1910, with industrial growth from this time until the 1960s establishing the city as a manufacturing centre for the state, and the population grew to over 100,000 by the mid-1960s. Population increases during the 21st century were largely due to growth in service industries, as the manufacturing sector has declined. Redevelopment of the inner city has occurred since the 1990s, as well as gentrification of inner suburbs, and currently has a population growth rate higher than the national average.

Today, Geelong stands as an emerging healthcare, education and advanced manufacturing centre. The city's economy is shifting quickly, and, despite experiencing the drawbacks of losing much of its heavy manufacturing, it is seeing much growth in other tertiary sectors, positioning itself as one of the leading non-capital Australian cities. It is now Australia's second fastest-growing city. Geelong is regarded as the "Gateway City" due to its critical location to surrounding western Victorian regional centres, providing a transport corridor for surrounding regions to the state capital Melbourne. It is also home to the Geelong Football Club, the second-oldest club in the Australian Football League.

The name Geelong comes from Djilang, used by the Wadawurrung traditional owners of the area at the time of settlement.^{[citation needed]}

The area of Geelong and the Bellarine Peninsula are the traditional lands of the Wadawurrung (Wathaurong) Indigenous Australian tribe. The first non-Indigenous person recorded as visiting the region was Lieutenant John Murray, who commanded the brig HMS Lady Nelson. After anchoring outside Port Phillip Heads (the narrow entrance to Port Phillip, onto which both Geelong and Melbourne now front), on 1 February 1802, he sent a small boat with six men to explore. Led by John Bowen, they explored the immediate area, returning to Lady Nelson on 4 February. On reporting favourable findings, Lady Nelson entered Port Phillip on 14 February, and did not leave until 12 March. During this time, Murray explored the Geelong area and, whilst on the far side of the bay, claimed the entire area for Britain. He named the bay Port King, after Philip Gidley King, then Governor of New South Wales. Governor King later renamed the bay Port Phillip after the first governor of New South Wales, Arthur Phillip. Arriving not long after Murray was Matthew Flinders, who entered Port Phillip on 27 April 1802. He charted the entire bay, including the Geelong area, believing he was the first to sight the huge expanse of water, but in a rush to reach Sydney before winter set in, he left Port Phillip on 3 May.

In January 1803, Surveyor-General Charles Grimes arrived at Port Phillip in the sloop Cumberland and mapped the area, including the future site of Geelong, but reported the area was unfavourable for settlement and returned to Sydney on 27 February. In October of the same year, HMS Calcutta led by Lieutenant Colonel David Collins arrived in the bay to establish the Sullivan Bay penal colony. Collins was dissatisfied with the area chosen, and sent a small party led by First Lieutenant J.H. Tuckey to investigate alternative sites. The party spent 22 to 27 October on the north shore of Corio Bay, where the first Aboriginal death at the hands of a European in Victoria occurred.

The next European visit to the area was by the explorers Hamilton Hume and William Hovell. They reached the northern edge of Corio Bay – the area of Port Phillip that Geelong now fronts – on 16 December 1824, and it was at this time they reported that the Aboriginals called the area Corayo, the bay being called Djillong. Hume and Hovell had been contracted to travel overland from Sydney to Port Phillip, and having achieved this, they stayed the night and began their return journey two days later on 18 December.