Idanha-a-Nova is a town and municipality located in the district of Castelo Branco in east-central Portugal. It serves as a border municipality with Spain and covers an area of 1416.34 km2. Due to its size and demographics, it is one of the largest and least densely populated municipalities in Portugal, and it was identified as the first Portuguese municipality by population ageing.
The town's name was established in 1219 when King Afonso II confirmed its charter, renaming the village Idanha-a-Nova to distinguish it from the older settlement of Idanha located 18 kilometers away. The local municipal holiday is observed on the Monday occurring 15 days after Easter.