Microelectronic devices include stadium structures within a stack structure and substantially symmetrically distributed between a first pillar structure and a second pillar structure, each of which vertically extends through the stack structure. The stack structure includes a vertically alternating sequence of insulative materials and conductive materials arranged in tiers. Each of the stadium structures includes staircase structures having steps including lateral ends of some of the tiers. The substantially symmetrical distribution of the stadium structures, and fill material adjacent such structures, may substantially balance material stresses to avoid or minimize bending of the adjacent pillars. Related methods and systems are also disclosed.