The town lies between Ovada and Gavi, in the northern Ligurian Apennines, and its municipal territory even borders Genoa along an Apennine ridge—the closest point in Piedmont to the sea, just seven kilometers away.

Bosio became part of Piedmont only after the Rattazzi Law of 1859, enacted to reorganize the administrative map of the entire Savoy state.

The village itself sits at an altitude of nearly 360 meters, while the highest point of its territory reaches 1,080 meters.

Bosio is included in the Capanne di Marcarolo Regional Nature Park, with Monte Tobbio at its center. This steep and barren mountain is topped by a church dedicated to Our Lady of Caravaggio, which has been owned by the Italian Alpine Club (CAI) since 1897.

In 1944, Bosio was the scene of brutal reprisals by German and Fascist forces against local partisans at Cascina Benedicta, an ancient medieval monastery dating back to the year 1000. The partisans had chosen the site as a refuge and meeting place, but in April 1944, German troops attacked the monastery violently, killing 75 partisans in combat, shooting 97 on the spot, and continuing the roundup across the surrounding countryside and mountains. The Germans then blew up the monastery, which now stands in ruins, preserved as a memorial site.

Just outside the village, Big Bench No. 84 was installed in 2019. Painted bright orange, it occupies a panoramic spot on Ronco hill, surrounded by vineyards and fruit trees.