A method used in forming a memory array comprising strings of memory cells comprises forming a stack comprising vertically-alternating first tiers and second tiers above a substrate. Horizontally-elongated trenches are formed into the stack to form laterally-spaced memory-block regions. Catalytic material is formed in a bottom region of individual of the trenches. Metal material is electrolessly deposited onto a catalytic surface of the catalytic material to individually fill at least a majority of remaining volume of the individual trenches. Channel-material strings are formed and extend through the first tiers and the second tiers. Other embodiments, including structure independent of method, are disclosed.