Nowy Tomyśl County (Polish: powiat nowotomyski) is a unit of territorial administration and local government (powiat) in Greater Poland Voivodeship, west-central Poland. It was created on January 1, 1999 as a result of the Local Government Reorganization Act of 1998. Its administrative seat and largest town is Nowy Tomyśl, which lies 55 kilometres (34 mi) west of the regional capital Poznań. The county contains three other towns: Opalenica, 20 km (12 mi) east of Nowy Tomyśl, Zbąszyń, 17 km (11 mi) south-west of Nowy Tomyśl, and Lwówek, 16 km (10 mi) north of Nowy Tomyśl.
The county covers an area of 1,011.67 square kilometres (390.6 sq mi). As of 2006 its total population is 71,817, out of which the population of Nowy Tomyśl is 15,225, that of Opalenica is 9,104, that of Zbąszyń is 7,300, that of Lwówek is 2,909, and the rural population is 37,279.