Nowy Tomyśl County is a unit of territorial administration and local government in Greater Poland Voivodeship, west-central 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 Nowy Tomyśl, which lies 55 kilometres west of the regional capital Poznań. The county contains three other towns: Opalenica, 20 km east of Nowy Tomyśl, Zbąszyń, 17 km south-west of Nowy Tomyśl, and Lwówek, 16 km north of Nowy Tomyśl.
The county covers an area of 1,011.67 square kilometres. 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.