Transcription errors are far from rare within indexes of genealogical sources, not least in census records. Poor handwriting and misunderstanding information can cause all sorts of mistakes to be made within the original records themselves, as well as the indexes compiled at a later date.
A perhaps surprisingly common error is the indexing of “Middlesex” to read “Mexico”. Type in Mexico as a place of birth within any census search engine, and many results are given. But look closely, and how many suggest indexing errors? For example, with the 1901 census surely “Holborn Mexico” and “Southall Mexico” and the numerous entries relating to “London Mexico” all refer to the county of Middlesex?
So take care when examining indexes, and always look at the original!