Yes, we have been to Cornelia and there is not much to report. It is located about 30km south of Villiers, geo position: 27.234°S, 28.8497°E, 1593m abmsl. They have a nice church and for a change it has no fence around it and no locked gate. And than there are a few sand stone houses. The one in the picture would be nice restore.
About the history? There is not much, the reference merely states that the town was proclaimed in 1917 and became a municipality in 1923. The beginnings of the settlement were possibly earlier, there is a website that states that the first buildings went up at around 1875. The name of the town is from the second wife of the Free Sate president Reitz.
Only after the visit when checking the reference did I notice that we missed the fossil site about 10 km out of town. Here they found fossils of the early fauna of the highveld, I think 4 to 5 Million years ago. And there is also some info on humanoid bones, about 1 Million years old. But let's not worry, its most likely not possible to visit the site.
Reference: 'Standard Encyclopedia of Southern Africa', 1972