Opoczno County (powiat opoczyński) is a unit of territorial administration and local government (powiat) in Łódź Voivodeship, south-east Poland. It came into being on January 1, 1999, as a result of the Polish local government reforms passed in 1998. Its administrative seat and largest town is Opoczno, which lies 72 km south-east of the regional capital Łódź. The only other town in the county is Drzewica, lying 15 km north-east of Opoczno.
The county covers an area of 1038.77 km2. As of 2009 its total population is 78,467, out of which the population of Opoczno is 21,635 (2016), that of Drzewica is 3,913 (2016), and the rural population is 52,006.
Opoczno County is bordered by Przysucha County to the east, Końskie County to the south, Piotrków County to the west and Tomaszów Mazowiecki County to the north-west.