Microelectronic devices include a stack structure with a vertically alternating sequence of insulative structures and conductive structures arranged in tiers. A series of slit structures extends through the stack structure and divides the stack structure into a series of blocks. In a progressed portion of the series of blocks, each block comprises an array of pillars extending through the stack structure of the block. Also, each block—in the progressed portion—has a different block width than a block width of a neighboring block of the progressed portion of the series of blocks. At least one pillar, of the pillars of the array of pillars in the progressed portion, exhibits bending. Related methods and electronic systems are also disclosed.