This paper presents a historical model of non-financial corporate cash demand. Although 1947-1971 data are used here, in another article the writer has applied the same formulation to earlier years. The main thrust of the argument is that (1) Very large firms have had a different demand-forcash function from other firms. (2) When the business population changes substantially, relative increases or decreases in numbers tend to be greater where entry and exit are easier, among smaller firms. Thus, business structure has changed with business population. (3) Aggregate corporate cash holding is therefore influenced over the long run by changes in corporate population, as well as by changes in aggregate receipts, interest rates, and cyclical factors. Empirical estimates indicate that the sector's postwar holding of cash, relative to receipts, was substantially less than it would have been if the composition of the corporate population had not changed as the number of firms exploded after 1947.