From the Oxford dictionary:
Definition of whence in English: interrogative adverb
From what place or source: whence does Parliament derive this power?
More example sentences
1From which; from where: the Ural mountains, whence the ore is procured
1.1To the place from which: he will be sent back whence he came
More example sentences
1.2As a consequence of which: whence it followed that the strategies were obsolete
More example sentences
Origin
Middle English whennes, from earlier whenne (from Old English hwanon, of Germanic origin) + -s3 (later respelled -ce to denote the unvoiced sound).
Usage
Strictly speaking, whence means ‘from what place’, as in whence did you come? Thus, the preposition from in from whence did you come? is redundant, and its use is considered incorrect by some. The use with from is very common, though, and has been used by reputable writers since the 14th century. It is now broadly accepted in standard English.