It is located in the province of Southern Finland and is part of the Tavastia Proper region. The municipality had a population of 2,378 (30 November 2008) and covered an area of 290.85 square kilometres (112.30 sq mi) of which 12.32 km2 (4.76 sq mi) is water. The population density is 8.54 inhabitants per square kilometre (22.1/sq mi).
The municipality is unilingually Finnish. The municipality has previously also been known as "Rengo" in Swedish documents, but is today referred to as "Renko" also in Swedish.