Last name?

It is really pretty simple, a surname is actually just a word and words come from languages to the "Origin" is a language, which in this case it Spanish. It has little to nothing to do with the Jewish Religion, other that perhaps 2-3 names that have been traditionally Jewish. The name you are asking about is not one of them. If you have questions about being Jewish, suggest that you research until you actually find someone in your family who was Jewish.

You have to understand Christians, Jews and the village atheist frequently wound up with the same surname. Surnames originally were not started to identify a person as a member of a family but just to better identify him on records. Too many men with the same given name in the same town or village and they just had to have a way of sorting them out.. When they got through it wasn't impossible for legitimate sons of the same man to wind up with a different surname and still each could have shared his with others with no known relationship.

Words which names are do not tell you what country nor religion, what they can tell you is the language the person spoke, heard or was influenced by when taking/being given the name........ Spanish was a language ( and still is) which is heard, spoken or influenced many countries of the world, any one of which the name could have "originated" in and those people could have been of any religion

Mercado is a portuguese origin name. But after doing my research on the name it is cited with respect to Jews and Crypto-Jews in at least 16 bibliographical, documentary, or electronic references.

You seem to be exceptionally stressed over something of no importance. It is a simple Spanish word no doubt used by many different kinds of Spanish people. You need to think about why you think this is so important.

It might be Sephardic.Sephardic Jews have ancestors from Spain and Portugal

I copy and paste this every few weeks, when someone asks if a surname was Christan or Jewish.

With three exceptions - "Levi", "Cantor" and "Cohen", all with many spelling variations - there are no "Jewish" surnames.

With some exceptions, there are no "Christian" surnames, either. One exception is "Christian" itself; you may remember Fletcher Christian from the Mutiny of the Bounty. Others are "Cruz" and "Saint ----".

Every other European surname could be Jewish, Christian - or Druid, for that matter. There were Christians and Jews who worked as carpenters, millers and smiths. There were Christians and Jews who lived by a hill, river, marsh or green. There were Christians and Jews with strong arms ("Armstrong") and tall frames ("Longfellow"). There were Christians and Jews whose fathers were named John and William. ("Johnson","Williamson", "Williams", "Wilson").

Spain has and has had Jewish citizens. They are called Sephardic Jews.