Reigoldswil is a municipality in the district of Waldenburg in the canton of Basel-Country in Switzerland.
Reigoldswil is first mentioned in 1152 as Rigoltswilre.
Reigoldswil has an area, , of . Of this area, or 46.2% is used for agricultural purposes, while or 45.1% is forested. Of the rest of the land, or 8.1% is settled (buildings or roads), or 0.1% is either rivers or lakes.
Of the built up area, housing and buildings made up 4.2% and transportation infrastructure made up 2.8%. Out of the forested land, 41.5% of the total land area is heavily forested and 3.6% is covered with orchards or small clusters of trees. Of the agricultural land, 5.8% is used for growing crops and 32.9% is pastures, while 5.0% is used for orchards or vine crops and 2.5% is used for alpine pastures. All the water in the municipality is in lakes.
The municipality is located in the Waldenburg district, in the far Frenken valley. The current village grew out of three separate medieval villages, in the 18th century. It consists of the villages of Hofstetten-Chilchli, Mittelbiel and Unterbiel.
The blazon of the municipal coat of arms is Per fess, Or, an Eagle Vair, langued beaked and membered Gules, and Azure, a Bend wavy Argent.
Reigoldswil has a population () of . , 8.1% of the population are resident foreign nationals. Over the last 10 years (1997–2007) the population has changed at a rate of 4%.
Most of the population () speaks German (1,419 or 93.4%), with Albanian being second most common (23 or 1.5%) and French being third (20 or 1.3%). There are 2 people who speak Romansh.
the gender distribution of the population was 48.7% male and 51.3% female. The population was made up of 1,397 Swiss citizens (89.5% of the population), and 164 non-Swiss residents (10.5%) Of the population in the municipality 573 or about 37.7% were born in Reigoldswil and lived there in 2000. There were 393 or 25.9% who were born in the same canton, while 335 or 22.0% were born somewhere else in Switzerland, and 153 or 10.1% were born outside of Switzerland.