A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data
In theory, it's possible to write a macro that creates the check boxes and links them to the appropriate cells.
But I fear that creating and using over 30,000 check boxes would have a negative impact on performance and would be a nightmare to manage.
I'd simply enter an "x" or something like that in the cells, and use the COUNTA function to count non-blank cells.