Horta de Sant Joan is a village and municipality in the comarca of Terra Alta, in the autonomous community of Catalonia, Spain. It has a population of around 1,150.
The municipality lies within the Terra Alta comarca, a district in the province of Tarragona in southern Catalonia. As a municipality, it covers the village itself together with the surrounding rural area.
Its small population of roughly 1,150 makes it one of the many modest-sized municipalities that characterise the Terra Alta district.