Kostelac families are Croats and they are mostly from Otocac. In the past century, relatively most of Croatian residents bearing this family name were born in Otocac and Zagreb.
About 790 people with faimily name Kostelac live in Croatia today, in 320 households. There were 730 of them in the middle of the past century, and their number increased by 10 percent. They are located in the most of Croatian counties, in 35 cities and 74 other places, mostly in Prozor (145), Otocac (120), Zagreb (110), Svica (75), and in Kutina (25).