Origins, Meaning, & Early History (1200-1500)
A good place to start searching for background information on your surname is Wikipedia. There will be links to other websites, references, and sources such as Clan websites that will usually have a detailed history of your surname, it's meaning, and where it originated. Such information must be taken with a grain of salt but it is a useful starting point for your further research.
Specific websites that may prove useful include:
- The Irish Ancestors website created by John Grenham (and previously hosted by the Irish Times). You can search for your own surname here. It will give you some brief information about your surname. Be sure to explore the links in the menu bar on the left.
- Clans of Ireland website - this is an independent organisation established in 1989 with the purpose of creating and maintaining a Register of Irish Clans. The Patron is Michael D. Higgins, President of Ireland. The website has a Register of Clans with contact details and links to websites of individual clans.
- Irish Pedigrees: Origin and Stem of the Irish Nation by John O'Hart
- Irish Names and Surnames, by Patrick Woulfe (1906)
- The Irish And Anglo-Irish Landed Gentry, When Cromwell Came to Ireland, by John O'Hart
- The Irish Book of Arms: Genealogy and Heraldry from the Earliest Times, by Michael C. O'Laughlin
- The Book of Irish Families: Great & Small, by Michael C. O'Laughlin
- The Surnames of Ireland (1957, reprinted 1991)
- Irish Families (1957, reprinted 1985)
- More Irish Families (1970, reprinted 1996)
End of the Gaelic Clans (1500-1700)
The Tudor Fiants were administrative documents used in the process of conveying a title, office, right or pardon. These cover the period from 1521 (Henry VIII) to 1603 (Elizabeth I) and are available online. There are 120,000 people mentioned in these fiants. To give you a taste, you can read the fiant for the pardon of Grace O'Malley (the Pirate Queen) here.
The 1600's were a tumultuous time in Irish history marked by the Catholic Rebellion of 1641 and the subsequent conquest of Ireland by Oliver Cromwell. The old Gaelic clans were finally brought under the control of the English. Many people lost their land during this time, others fled Ireland and went into exile, some sold themselves as indentured servants, and others were sent as slaves to the Caribbean and the new American Colonies.
There are two excellent websites (both run by Trinity College, Dublin) that help tell the story of your family's surname during this time. You can check if anyone with your surname appeared in the depositions relating to the 1641 Rebellion, and details of any transfer in land ownership is beautifully described on The Down Survey of Ireland. This will help tell you where your family held land, the name of the local area, and it's location in both historical and present day maps. Another useful free online source is the 1659 census which nicely compliments the other two sources (also available here).
The Silent Century (1700-1800)
The 1700's represents a large genealogical gap for Ireland - it is the "silent century". There are much fewer records available for this period than there are for the 1800's and 1900's. Many Irish people can trace their family tree back to 1800 but no further. This is the typical place where many ancestral lines end in a Brick Wall. However, resources that can prove helpful for performing a general search for your family name and it's location include:
- The Irish Ancestors website (mentioned above). A surname search will generate surname distribution maps based on Griffith's Valuation from the mid-1800's. This is a pay website (after 5 free searches) whereas the others below are completely free.
- Shane Wilson's website provides surname distribution maps based on Griffiths Valuation.
- Barry Griffin's website provides surname distribution maps based on the 1901 & 1911 census and also on the distribution of farmers in each census.
- The Forbears website gives you surname distribution maps based on the UK 1911 census.
- The PublicProfiler website used to be a very good source for surnames in Britain and the rest of the world but now appears to be defunct.
The Registry of Deeds lists many wills and land deeds from 1708 onwards - the LDS has these on microfilm (which have recently been digitised and are available onscreen at LDS-affiliated libraries). 
The Landed Estates database has lots of records relating to estates in the provinces of Connaught & Munster (Leinster and Ulster are not covered).
You can find what additional records are available at the following websites:
- PRONI (Public Record Office of Northern Ireland)
- Census substitutes are described on the Irish Ancestors website - 1500-1600 records and 1700-1800 records
Tracing Irish Ancestors who emigrated (1800-1865)
Many Irish emigrated during the 1800's and all that is recorded for their previous address in their new country is "Ireland".
For those who emigrated to the US, their earliest emigration records may be found on Passenger Lists and Ships' Manifests. The Irish Emigrant Database is a useful way of identifying records that may be found on some of the free Passenger List websites including:
- http://www.nationalarchives.gov.uk/records/looking-for-person/passengers.htm (many Irish travelled via the UK)
The Journal of the American-Irish Historical Society includes passenger lists, research articles, and other useful sources. Volumes 1–22 (through 1922) are available online for free -Hathi Digital Trust.
The Famine Irish Passenger Record Data File 1846–1851 has 604,596 persons who arrived in the Port of New York between 1846 and 1851.
Irish American newspapers can often be very useful in determining an Irish immigrant's town of birth - see Tom Kemp's explanation here - What Counties & Towns in Ireland Did Our Ancestors Come From?
The Emigrant Savings Bank, established in 1850 by members of the Irish Emigrant Society, in researching Irish ancestors. The records of the New York Emigrant Savings Bank are available on Ancestry.com, cover the period of 1850–1880 and may provide the town of origin in Ireland, as well as names of parents, siblings, spouses and children.
Modern History (1865-1940)
If you want to look for a specific person, the various resources available include the following:
Births, Marriages, & Deaths
- Civil Registration Records (1845 onwards for non-Catholics, 1865 onwards for everyone) - both www.irishgenealogy.ie and www.familysearch.org have a free search of the indexes. In addition, www.irishgenealogy.ie is gradually adding free digital images of the original certificates to their website. For any certificates that are not there (yet), you will need to visit your local LDS centre  where they have some of the certificates  on microfilm (free), which you can photograph on the screen or photocopy for a small fee; or write to the General Registry Office (GRO) in Co. Roscommon, Ireland, using this form and purchase photocopies of the certificates for 4 euro each).
- The IGI (International Genealogical Index) is another potential and complementary source of birth and church records. It sometimes has additional records not included on the main LDS familysearch website.
- Church Records (about 1800 onwards) - Rootsireland (index search is free but pay-per-view for transcriptions of the actual records 5 euro each) and IrishGenealogy (free index search, free transcriptions of records, & free scanned images of records). You can learn a lot from fiddling around with different search options.
- 1901 census
- 1911 census
- Griffiths Primary Valuation (mid 1800's)
- Cancelled Books of subsequent valuations (from the mid-1800's to the mid-1900's). You will need to visit the Valuation Office in Dublin in order to consult them (in colour) or order the black and white version on microfiche via your local LDS Family Research centre.
- Directories (early 1800's onwards) - these are a useful census substitute. They only record the head of the family but can be used sequentially to provide an approximate date of death of an individual or to track the change in land ownership within the family (e.g. from father to son) or outside of the family. Various directories are freely available online (see the Irish Ancestors Website and the Irish Directory Database, which has links to over 1000 directories online, many free-of-charge). The National Library of Ireland (NLI) has some directories but the Dublin City Library and Archive (DCLA) has a more complete set. Both can be consulted free of charge at the library itself.
- Tithe Applotement Books - available free from the National Archives of Ireland website. They cover the period 1823-1837 approximately.
- Always try a Google Books search for your ancestors - you never know what has been written about them in the past! Many books are available in the entirety, others only partially.
- Newspapers often have birth, marriage and death notices and may also contain fabulous information about ancestors who have ended up in the public eye, usually for all the wrong reasons. Websites of Irish relevance include www.irishnewsarchive.com, www.britishnewspaperarchive.co.uk, the Irish Times digital archive, and some English newspapers such as The Times (some may be accessible from your local LDS centre or your local library or via your local library's website from the comfort of your own home) - search is usually free, articles are usually pay-per-view.
- Glasnevin cemetery (Dublin's main cemetery) - an invaluable resource for anyone whose Catholic ancestors lived in Dublin. It has over 1 million records. Make sure to tick the box for all people in the grave and to order the actual register entry itself as this contains additional information.
- Many international websites have burial records for Irish graveyards, but coverage is by no means comprehensive. Explore the following: www.historicgraves.ie, www.findagrave.com, www.deceasedonline.com, www.billiongraves.com, www.discovereverafter.com, www.interment.net, and various other smaller websites (Google them).
DNA testing & your surname
Sometimes a DNA test is the tool that will help you break down a brick wall. To check if anyone with your surname has already been DNA-tested, and to see if there is a DNA project associated with your surname, go to www.familytreedna.com and enter your surname (and its variants) in the box below "Search Your Last Name" (on the right side of the home page). Be sure to click on any links that come up to explore further.
A handout from Roz McCutcheon on Irish sources from RootsTech 2015 - http://www.irishancestors.ie/wp-content/uploads/2015/02/Roz-McCutcheon-at-RootsTech2015.pdf
1) LDS stands for Latter Day Saints, an abbreviation of The Church of Jesus Christ of the Latter Day Saints, otherwise known as the Mormons. They have created a huge genealogical resource, particularly for Irish records, and as well as running the free genealogical website www.familysearch.org, they also have many Family History Centres throughout the world where you can order and view microfilmed records from Ireland going back to the 1600's. Check out their website for more info.
2) The following gives a summary of the Irish BMD records that are available via your local LDS centre. Some of these microfilm reels will have to be ordered and this may take up to 6 weeks. However, this service is free. Any records that fall outside of these years will have to be ordered via the GRO at 4 euro per record.
- Birth certificates - 1864-1881, 1900-1913, and most of 1930, 1931, 1932, 1939
- Marriage certificates
- Church of Ireland - 1845, 1847, 1848, 1850, 1854, 1856, 1857, 1859
- all religions - 1864-1870
- Death certificates - 1864-1870