COUNT is not as straightforward as it might look. Many people think it counts the number of cells in a range, or the number of populated cells. But it doesn't. Instead, it counts the number of cells in a range that contain a numeric value. This will include dates, percentages etc. as well as your bog-standard numbers.
If the cells in your range contain the values 1, 2, 3, Y and 4, then the function will return the value 4, ignoring the Y. Blank cells will be similarly ignored. Similarly, it will ignore logical values (i.e. those that contain a TRUE/FALSE value). But cells containing a zero will be included in the count.
Range can be made up of a single range or a set of distinct ranges. If you're using a set of distinct ranges, they should be separated with commas.
=COUNT(A1:Q20): this will count the number of numeric cells between columns A and Q, in rows 1 through 20
=COUNT(A1,C5,D12,D15:D20): this will count the number of numeric cells the ranges specified