From the Wikipedia page 
Kharkiv Oblast (Ukrainian: Харківська область, translit. Charkivśka oblastj; also referred to as Kharkivshchyna – Ukrainian: Харківщина, Charkivščyna) is an oblast (province) in eastern Ukraine. The oblast borders Russia to the north, Luhansk Oblast to the east, Donetsk Oblast to the south-east, Dnipropetrovsk Oblast to the south-west, Poltava Oblast to the west and Sumy Oblast to the north-west. The area of the oblast is 31,400 km², corresponding to 5.2% of the total territory of Ukraine. Population: 2,701, 188 (2017 est.)
The oblast is the third most populous province of Ukraine more than half of whom live in the city of Kharkiv, the oblast's administrative center. While the Russian language is primarily spoken in the cities of Kharkiv oblast, elsewhere in the oblast most inhabitants speak Ukrainian.