do.

Do. is the written abbreviation of ditto, and it does the same job as the ditto marks (" ") still used today. A census taker who wrote Penn. for the first person in a household might write do. for everyone else born there.

Read it carefully. It copies whatever is directly above it, which may be on a different family's line or at the bottom of the previous page. Indexers sometimes copy do. literally, so check the image when an index shows an odd birthplace or surname of "Do".