How Did Musical Notes Get Their Names?

Notation clearly begun and developed in parallel with music theory, because you cannot record what notes are being used if you have no names for the notes, or way of identifying what relationships are between the notes. Hence, as the concepts of scales and keys began to take shape, so notes started to be named.

Where do the names of music notes come from?

The first Western system of functional names for the musical notes was introduced by Guido of Arezzo (c. 991 – after 1033), using the beginning syllables of the first six musical lines of the Latin hymn Ut queant laxis. The original sequence was Ut Re Mi Fa Sol La, where each verse started a scale note higher.

How did the notes get their letters?

It's basically singing the same thing in different keys. For example, if you're singing the major scale in C major your scale would be C,D,E,F,G,A,B,C but if you're in D major your Do,Re,Mi,Fa,Sol,La,Si,Do would be D,E,F♯,G,A,B,C♯,D. They're both used in different parts of the world.