William Allen Neilson (1869 - 1946) was a U.S. (Scottish-born) educator, writer and lexicographer. He was president of Smith College between 1917 and 1939.

He was born in Doune, Scotland . He taught at Byrn Mawr College from 1898 to 1900, Harvard from 1900 to 1904, Columbia from 1904 to 1906, and Harvard again from 1906 to 1917. He wrote on poetry and William Shakespeare and was the editor of Webster's New International Dictionary, Second Edition (1934).