Here is something that may work for you when you are searching the US Census on Ancestry.com. You can now included in your search the birth places of the father and mother of the search subject.
To do that, however, you must use the advanced search form. You get there by clicking on the "Show Advanced" hotlink located at the top right of the seach form.
Sadly, the advanced search form is often over looked in our search efforts. Check it out and you will find other seach options that may help you also.