The municipality of Osoppo contains the frazioni (subdivisions, mainly villages and hamlets) Pineta and Rivoli.

Osoppo borders the following municipalities: Buja, Forgaria nel Friuli, Gemona del Friuli, Majano, San Daniele del Friuli, Trasaghis.

Osoppo hosts a large fortress (La Fortezza o Rocca di Osoppo), now an historical attraction. It played a large role in the defense of Venice against the Austrians in the late 1850s during the time of the Italian Risorgimento, the struggle for the unification and independence of Italy. It was shortly after one of the main battles at this fortress that Leonardo Andervolti composed his famous treatise, Meritorious Champions of Italian Independence, a eulogy to a mythical figure, Enrico Ulissi. The patriot Andervolti, from nearby Spilimbergo, remains famous in the collective imagination of Italians for his heroic struggles in this time period.