Well I'm from South Africa (grandad Harold Allsobrook emigrated there from Lewes, Sussex after WWII). There are a few Allsobrooks here and there in the UK and no doubt a bunch sailed over to the USA way back and (as Americans will do) got the speling wrong! But where'd they come from before that? Heard some vague story once that they were jews which arrived via Holland or something..... Not a particularly English name is it? Sounds kinda Germanic/Teutonic.