=SUM(IF(MONTH($A$2:$A$20)=11,1,0))
Confirm the formula by pressing [b]Ctrl + Shift + Enter, Not Just Enter..
Adjust the range as per requirement.. Hope it will works.. in any version of excel and in any language also.. :)
EDIT:
I just read the heading of the post.. It consist TEXT word..
So please give one more try..
=SUM(IF(ISNUMBER(SEARCH("Nov",A2:A20)),1,0))