An organic light-emitting display device includes a substrate having a display area surrounding a through area, and a peripheral area between the through and display areas, a light-emitting element on the display area, a first dam on the peripheral area and surrounding the through area, a first protruding pattern on the first dam and protruding toward the display area from the first dam to define an undercut region, a boundary portion extending from the display area toward the first dam, the boundary portion being spaced apart from the first dam to define a first receiving space therebetween, and an encapsulation layer continuously extending from the display area to the peripheral area, the encapsulation layer including at least one organic layer with a first filling portion filling at least part of the first receiving space and protruding toward the first dam to be aligned with the undercut region.