If you're looking for a big Australian town not on the coast Ballarat would be one. Towns can service the rural sector even if they are on the coast. See the link below (50 largest Urban Centres by population) for places to choose from.
If the Outback is defined as that part of Australia which is remote and semi-arid, then the answer would be Kalgoorlie-Boulder, in Western Australia. This major gold-mining centre in the remote desert area of the state has a pulsation if about 33 000 as of 2013. Alice Springs, in central Australia, would be the next largest outback city, with a population of around 28 000.
Dubbo is a large regional city in western New South Wales, with around 36 000, but it is not really remote enough to be considered "Outback".
The Australian Outback is probably the largest part of Australia.
There is no "main" city of the outback. Alice Springs in central Australia is probably regarded as the main city of the outback, though it is really a large town. Similarly, Kalgoorlie-Boulder in the heart of Western Australia's gold mining country is a significant city (with more of the feel of a large town) that is certainly located in the outback.
Oklahoma City is the largest town in Oklahoma.
Longreach Queensland
Warwick is the County Town - the seat of Local Government - and Nuneaton is the largest town.
The largest town in Fiji is Nausori while the smallest town in Fiji is Navua.
The largest town in southern Otago is Balclutha.
Queenstown is the largest town at Lake Wakatipu
Birdsville
Down town
The Town of Brookhaven
New York City is the largest "town" in the state of New York.