Jirnsum (Dutch: Irnsum[3]) is a village in Leeuwarden municipality in the province of Friesland, the Netherlands.

[4] The village was first mentioned between 1399 and 1401 as Yrntzom, and means "settlement of the people of Irin".

[5] Jirnsum developed as a terp (artificial living mound) living along the Boorne [nl] river.

The Mennonite church dates from 1684 and received its current form in 1866.

[8] Before 2014, Jirnsum was part of Boarnsterhim municipality and before 1984 it belonged to Rauwerdhem.