Jarnostaw [jarˈnɔstaf] is a village in the administrative district of Gmina Sośnie, within Ostrów Wielkopolski County, Greater Poland Voivodeship, in west-central Poland. It lies approximately 5 kilometres (3 mi) west of Sośnie, 22 km (14 mi) south-west of Ostrów Wielkopolski, and 112 km (70 mi) south-east of the regional capital Poznań.