The word "tobacco" by itself is not countable. You can not say "1 tobacco, 2 tobaccos, 3 tobaccos, etc." "Tobacco" is counted by the plant, so you would say "1 tobacco plant, 2 tobacco plants." You could also count it as a "stalk of tobacco." (1 stalk of tobacco, 2 stalks of tobacco, etc.). How you phrase it, will depend slightly on the context it is used in.

It's usually uncountable, but could be pluralized to refer to varieties or kinds of tobacco. The plural is spelled with no "e" -- tobaccos. See the entry in the Oxford: https://en.oxforddictionaries.com/definition/tobacco