William Sweetland Dallas FLS (1824–1890) was a British zoologist and curator. He curated collections at the British Museum and the Yorkshire Philosophical Society, and was editor of the Popular Science Review.

He was appointed Keeper of the Yorkshire Museum in 1858, at the age of 31 and already married with four children at the time.^[1][2] Dallas was an editor and translator for the Zoological Record, the Annals and Magazine of Natural History and the Popular Science Review. In 1868 he was elected to the post of Assistant Secretary of the Geological Society, resulting in his resignation from the role of Keeper.^[1]

Notably, he translated Facts and Arguments for Darwin by German biologist Fritz Müller into English.^[3] He also translated Karl Theodor Ernst von Siebold's Wahre Parthenogenesis bei Schmetterlingen und Bienen (1856) into English as On a true parthenogenesis in moths and bees^[4] and created the index for Charles Darwin's The Variation of Animals and Plants Under Domestication.

Dallas was elected a member of the Linnean Society in 1849.^[1]

He died at Burlington House, Piccadilly on 29 May 1890 and was buried at West Norwood Cemetery.