A method used in forming a memory array comprising strings of memory cells comprises forming a lower portion of a stack that will comprise vertically-alternating first tiers and second tiers on a substrate. The stack comprises laterally-spaced memory-block regions, Material of the first tiers is of different composition from material of the second tiers. Horizontally-elongated lines are formed in the lower portion that are individually between immediately-laterally-adjacent of the memory-block regions. The lines comprise sacrificial material. The lines individually comprise laterally-opposing projections longitudinally therealong in a lowest of the first tiers. The vertically-alternating first tiers and second tiers of an upper portion of the stack are formed above the lower portion and the lines, and channel-material strings are formed that extend through the first tiers and the second tiers in the upper portion to the lower portion. Horizontally-elongated trenches are formed into the stack that are individually between the immediately-laterally-adjacent memory-block regions and extend to the line there-between. The sacrificial material of the lines and projections is removed through the trenches. Intervening material is formed in the trenches and void-spaces left as a result of the removing of the sacrificial material of the lines. Other embodiments are disclosed.