How To Follow A Migrant Ancestor Paper Trail

How do I follow a migrant paper trail?

You can do it in one of two ways. You can either track them back from the point where you first found them in the country, or you can track them from where they were last known to be in the country of departure. The obvious main source would be the ship's passenger lists, and many of these have now been indexed and made available online with digital images. Also, you could have a look at the census returns since the nineteenth century, immigrant or emigrants, and find out when they first appeared in an early 10 yearly census return, and when they last appear in the place from which they departed. That will pinpoint the dates of departure down to within a decade, at least.