Riedholz is a municipality in the district of Lebern in the canton of Solothurn in Switzerland. In 2011 Niederwil merged into Riedholz. Riedholz is first mentioned in 1367 as im Rietholz. Niederwil is first mentioned in 1292 as Lomolzwile. Following the merger, the new, larger municipality had an area () of . 43.6% was used for agricultural purposes and 39% was forested. Settlement areas took up 14.6% and the total unproductive area took up 2.8% of the total. Riedholz had an area, before the merger in , of . Of this area, or 36.4% is used for agricultural purposes, while or 40.7% is forested. Of the rest of the land, or 19.6% is settled (buildings or roads), or 3.9% is either rivers or lakes. Of the built up area, industrial buildings made up 2.7% of the total area while housing and buildings made up 8.8% and transportation infrastructure made up 5.9%. Power and water infrastructure as well as other special developed areas made up 1.2% of the area Out of the forested land, all of the forested land area is covered with heavy forests. Of the agricultural land, 22.3% is used for growing crops and 12.7% is pastures, while 1.4% is used for orchards or vine crops. All the water in the municipality is flowing water. The municipality is located in the Lebern district, between a moraine and the Aare river. It consists of the village of Riedholz and Niederwil as well as scattered hamlets and individual settlements, including Attisholz which has had a thermal bath since the 15th Century. The blazon of the municipal coat of arms is Or a Fir Tree eradicated Vert. Riedholz has a population () of . , 8.2% of the population are resident foreign nationals. Over the last 10 years (1999–2009 ) the population has changed at a rate of 12.5%. Most of the population () speaks German (1,427 or 95.8%), with Italian being second most common (12 or 0.8%) and Albanian being third (11 or 0.7%). There are 7 people who speak French and 2 people who speak Romansh. the gender distribution of the population was 49.5% male and 50.5% female.