Hi,

If by "blank" you mean empty (and so not cells which appear empty but which actually contain the null string "", e.g. as a result of formulas in those cells), then you can use:

=COUNTA(Sheet1:Sheet200!D:D)

where Sheet1 and Sheet200 should be replaced with the names of the leftmost and rightmost worksheets within the workbook respectively.

If null strings are in fact present, you'll require a different solution. Let me know.

Regards