Boštanj is a formerly independent settlement in the southern part of the village of Veliko Mlačevo in central Slovenia. It belongs to the Municipality of Grosuplje. It is part of the traditional region of Lower Carniola and is now included with the rest of the municipality in the Central Slovenia Statistical Region.

The Blagaj family or Blagay were a Croatian noble family, hereditary counts that were a cadet branch of the medieval Babonić family, and named after their estate of Blagaj on the Sana in the 14th century. Over the course of the Croatian-Ottoman wars, they migrated to the northwest and by the end of the 16th century became part of Austrian and Slovenian nobility. They went extinct in the 19th century.