Where did all the last names we have come come? | AskHistorians Archive Observer

This depends on the surname, as different surnames have different origins, but a great many surnames originate as indicating (a) familial lineage, (b) place of origin, (c) profession, or sometimes (d) a physical characteristic.

Professions are the easiest: John Smith originates as, literally, John the smith; smithing was his profession. Fisher, Tailor, Weaver, Miller, Carpenter, Shoemaker, etc. all have the same origins.

Parental lineage is also obvious in some contexts: Bill Johnson = "Bill, son of John". Similarly, Bill O'Brian = "Bill of Brian", meaning "Bill, son of Brian". MacDonald = "son of Donald", D'Antonio = "son of Antonio", Rodriguez = "son of Rodrigo", and my favorite: the weighlifter Magnus ver Magnusson's name literally means "Magnus, son of the son of Magnus"

And since O', Mc, Mac, D', De, ver, von, -uez, and many others all mean "of" or "from", they can also be used to indicate a place they are from rather than a parent. Leonardo Da Vinci, for instance, means "Leonardo of Vinci", because he was literally from the town of Vinci.

Physical characteristics aren't as common, but still, there are plenty. The Slavic name "Plesko", for instance, means "bald", so Steve Plesko = "Steve the bald".

First of all, last names are not universal. There are entire cultures where the idea of a single surname passed down from father to children over generations is either the exception or unknown. In Iceland, for example, people have second names but they don't usually use them, and the second name is individual, not familial: Thor Magnússon's son might be legally named Carl Thorssen and his daughter Helgú Thorsdottir, but even formally the children would be known only as Carl and Helgú unless there was a need to differentiate them from another Carl or Helgú.

Western surnames can be classified in many (oh so many) ways, but I like to break them down into five large categories depending on what they're based on:

First names. Despite what's often believed, this does not always (or even often) mean "father's name". A surname may be based on the original adopter's father's name (Johnson, Wilson), but it might also refer to a mother (Madison), guardian/head of household such as a grandfather or uncle (possibly Adams), clan leader (McKinley), employer, distant ancestor, mythical ancestor, favourite saint (a lot of English Thomases arise from this), king, landlord, or even former owner. I might as well point out here that at least in English, matronymic surnames were never given to bastards; bastards weren’t allowed to name themselves after their parents, and early on weren't allowed surnames at all. Matronyms were instead given to sons born after their father's deaths, which explains why England is so rife with them.
Occupation. Fairly obvious (Carter, Tyler, Taylor) but sometimes tricky. Smythe, for instance, might sound like a froufrou reimagining of Smith, but it can also be a locational surname meaning "lives near the smithy".
Locational, which can be divided into "specific place name" like Washington, Lincoln, or Clinton, or "general descriptive names" like Polk (originally Pollock, meaning "fish pond") or Roosevelt ("flower field"). The general rule is that specific place names were used either by the ancestral landowners or by people who left the village for the big city, while general descriptive names were used by tenant farmers, yeomen, villeins, etc. to describe where their land was. The guy who took the name Garfield (or Gore) farmed a triangular plot of land, while Ford lived near the ford.
Nicknames. Can be based on appearance like Grant ("big") or personality like Truman ("true man", probably meaning loyal or honest).
Ornamental. These are uncommon in English. You mainly find them among peoples forced to adopt surnames in the 19th or early 20th century, such as Central European Jews, some Dutch, and Scandinavians. Jewish examples include Morgenstern ("morning star"), Safire ("sapphire"), and Mandelbaum ("almond tree"); Scandinavian examples include Lindburgh ("linden mountain") or Alstrom ("alder stream").

That all said, names aren't set in stone. They change over the generations. Mitt Romney is a good example; seven generations back the family surname was Rumley. In Scotland and Ireland, whether a family is a "Mac" or a "Mc" has more to do with the preference of the (often English) official who first wrote the name down than anything else; there are cases where one brother is a Mc, the next is a Mac, the third is a Mag, and a cousin is a M'!