Rheinfelden District lies in the northwest of the canton of Aargau in Switzerland, in the Fricktal region.

The Rheinfelden district has an area, as of 2009[update], of 111.98 square kilometres (43.24 sq mi).

Of the rest of the land, 14.96 km2 (5.78 sq mi) or 13.4% is settled (buildings or roads).

[4] From the 2000 census[update], 14,982 or 40.2% were Roman Catholic, while 11,153 or 29.9% belonged to the Swiss Reformed Church.

Of the rest of the population, there were 2 474 who belonged to the Christian Catholic faith.