Aalsum (West Frisian: Ealsum) is a village in the Dutch province of Friesland. It is located in the municipality Noardeast-Fryslân, about 1 km north of Dokkum. It had a population of around 125 in January 2017 Aalsum is built on a partially excavated terp, around a church originally dedicated to St. Catherine of Alexandria, which dates back to approximately 1200 AD.