Like any other surname it is a word and all words come from languages NOT countries, so you will have to research the records of the individual people who used that surname to see where they came from, as surname hunting will not tell you

There are NO LIVING DESCENDANTS of Abraham Lincoln. Your research is flawed.
there are some relatives, but no descendants.
http://www.daily-jeff.com/local%20news/2...
(and the headline for this story is not correct either)

Because we live in a male-dominated society. In the USA, women couldn't even vote until 1918. Children have to have one name or the other, unless, 4 generations down the line, they have 16 last names with hyphens in them. Men won out.

When you start to study history you'll find lots of instances where women get the short end of the stick. Children's surnames are just one of thousands of instances.

Depends which country you are in. You can see where the death was registered on the FBMD database if you are in the UK which gives a rough indication. You may be able to consult a local paper archive which might carry the announcement.

http://www.freebmd.org.uk/

You start with yourself and work back, one generation at a time. Since your parents and grandparents are (probably) living, they won't be in the historical records. So, you'd ask them who their parents and grandparents were; names, birth date and place, marriage date and place, death date and place, spouse's name. Once you collected that you'd look up the people you had who have been dead for 40 years or more to see if Ancestry had anything on them. Ancestry has less on Ireland than they do on the USA, but you might find things.

https://familysearch.org/search
is free and has a lot; not as much as Ancestry, but a lot, and, again, it is free.

You work back until you find Oscar was one of your ancestor's cousins or you get stuck.

One word of caution - ignore the public family trees that have less than 5 source citations, and check those that do. I have seen source citations that have three obviously different individuals with the same name lumped together as one person. Stick to the records, use the public family trees as clues, and be very suspicious.

Oscar was gay and had no children. His brother had just one child, a daughter who was a lesbian and had no children. Oscar's father was born in 1815, so if you are related to Oscar it will be through a sibling of his father, and finding people that far back - at a rough guess, the siblings were born 1805 - 1825 - is a real chore.

Don't expect to finish in the 14 day free trial. From your other questions, you are a teen. 99.999% of teens who ask about genealogy here lose interest when they find out research is work, like homework, and takes more than an hour. You might be the exception. You might also have quit reading three paragraphs ago.

Bsst wishes, and if you find something interesting, please let me know.

No way of knowing without doing basic research on YOUR family. Start with your parents and work backwards. Look for birth/marriage/immigration and census records. They'll point you in the right direction.