Joadja is a Historic Town (ruin) on the New South Wales Heritage Register in the Southern Highlands of New South Wales, Australia, in Wingecarribee Shire.
It was a thriving mining town between 1870–1911. It was home for approximately 1,200 people, many of whom were skilled immigrants from Scotland. After managing for ten years using bullock teams for transport, a railway was allowed and was connected to the nearby town of Mittagong by a narrow gauge railway that terminated adjacent to the main Southern Railway line in Mittagong. The town existed to mine oil shale from which kerosene was extracted by the Australian Kerosene Oil and Mineral Co. The process was superseded by conventional kerosene production from oil and the oil shale mining became uneconomical. By 1911, the town had become deserted as inhabitants relocated in search of work. The property was auctioned off that year to a private buyer. The fruit orchard, which included 6,700 trees continued to operate until 1924, exporting fruit for local and interstate consumption.
Situated in a deep valley, the town had limited access by road, instead exporting shale via a steep railway (incline) out of the valley. The passage into Joadja has improved greatly since then, with the gravel access road maintained annually. The township is still recognisable, despite the state of its ruins. The sandstone Joadja School, The School of Arts, the mines, houses at Carrington Row, refinery and even the cemetery remain as a testament to the community that lived in the valley more than a century ago.