Depending on the Kanji, or Japanese characters, used, the name Yoko can also mean "Chrysanthemum Child" or, "Ocean Child" (the latter being the case for the famous Yoko Ono). [noted -ed]
Can also mean "leaf child" or "big sea child".Used excessively in generations gone by, not as common in under 20 crowd (though still used). I've known lots of Yokos. It's almost as popular as Keiko, probably.