word usage - "It is the category where most of the processed data falls into" - is it correct?

Is the following sentence correct? I have some doubts about "category where ... fall into" phrase.

It is the category where most of the processed data falls into

Answer

Use of a preposition with where is non-Standard, because where itself stands for a preposition phrase. It's equivalent to in which or from which or at which or . . . which specific preposition is involved is inferred from the context. But the preposition is built in to the term where.

So if you're using your example in a context where Standard English is called for, you may say "the category where most of the processed data falls into" or "the category which most of the processed data falls into", but not "the category where most of the processed data falls into".

BUT: In some cases an extra preposition is necessary and acceptable. In particular, because where "defaults" to designating a location or a goal, adding from to designate an origin will often be necessary: "From where did you come?" (or "Where did you come from?"). Note, however, that this will not be necessary with a verb like get, which inherently implies an origin.

AND: It must also be acknowledged that in colloquial contexts it is not at all uncommon for a specific preposition to be added to make the specific meaning more explicit; and in these contexts it cannot be regarded as 'incorrect' or 'ungrammatical'.

Note, however, that such an 'extra' preposition is almost always stranded at the end of the clause; you will very rarely see it pied-piped to the position before where:

        ^{always OK} the category into which most of the processed data falls
        ^{usually OK} the category which most of the processed data falls into
^{colloquially OK} the category where most of the processed data falls into
               ^{not OK} the category into where most of the processed data falls