The Halloran and O'Halloran surname has been subject to different spellings in records.  A surname project  was commenced to permit others whose roots are Halloran or O'Halloran along with its many different spellings in the records to collaborate and discover relationships.  Many of these Halloran misspellings have been retained.   For example in my case, after researching the Hollarn surname in the U.S. many years ago it was recognized that the more correct surname for at least one branch is Halloran.  Another branch of Hollarn may have different origins.  And, Holland in rare cases may be another corruption of the "Halloran" surname.  

Joining:  Participants  in DNA testing with Halloran and O'Halloran ancestry are encouraged to join the project.  Variant spellings are also likely to be genetically related.  At this time, those who have tested Y-DNA, mtDNA, X-DNA, and autosomal DNA should feel welcome.  The best results for the surname study are expected to come from male Y-DNA Halloran participants.

The Hallorans of the north belong to a clan whose ancient origins seem to trace to Donegal in the early 100s A.D. and during historical periods of the 1700s and later in Ireland were located in County Galway,   This is likely to also apply to Hallorans of Mayo.  Some describe this as Northwest Irish or Irish Type I. Another sept of the Hallorans may have roots from Brian Boru in Cork, Kerry, Tipperary, and Limerick which after testing we might find is part of Irish Type III.  Likely a result in migration within Ireland, there are smaller numbers elsewhere.  The Diaspora emigrated from Ireland to other parts of the United Kingdom.  Additional areas include Australia, Canada, and a sizable emigration to the U.S.   In the U.S., communities with Hallorans are not surprisingly located in Boston, New York, a few in Appalachia, Wisconsin, Chicago, and California.  Over time, Hallorans are now located in much more diverse locales.   

Genealogy Research.  Tithe Applotment and Griffith Valuation records provide some of the earliest records on heads of household in Ireland.  Traditional records for births/baptisms are generally lacking for Halloran ancestry research before 1840 but there are a few records or parishes with earlier records.  Often in Ireland good records were not available until 1864 when civil records began for birth, marriages, and deaths.  Some earlier records exist in areas where emigration from Ireland occurred.  Extending traditional record research has been significantly complimented by DNA Analysis which can be helpful when normal traditional records have been exhausted and relationships lost.  Some Irish historical research identifies a few Hallorans recorded before 1800.

A Charles Halloran had a family in Salem, Massachusetts in late 1779.   A Will Halloran was a resident of Washington,D.C. in 1820.  In 1830 an Edward Halloran resided in Boston.  Finding Halloran's in U.S. records is rare before 1840.   The first good results for Halloran's in the U.S. begins with the 1860 Census.

A James Halloran appears to have been a British soldier and in Canada in or about 1802.  A bit unusual is Dick Halloran, listed as a black man, in Antigua as a slave of William Bowyer in 1817.  There is evidence that many Irish were "exported" from Ireland and England as indentured if not slaves in the 1600s and 1700s.  The earliest Halloran (L H Halloran) I found to immigrate (possibly unwillingly) to Australia was in 1819.  

The best if not the only complete Census available for Ireland is the 1901 and 1911 Census.  Some Hallorans appear in Census records that have survived and are archived in the U.K.  In the U.S., Hallorans are enumerated under several different spellings. 

DNA Contributions.  The Halloran DNA Surname project has been established to allow the Halloran and O'Halloran surname participants from around the world see if or how they are related to each other and through a common ancestor.

DNA results are permitting comparison with other Hallorans to determine relatives and relationships. This can be done by direct comparison and otherwise to determine genetic distance, then use of the concept of Time to Most Recent Common Ancestor (TMRCA), in finding genetic cousins.

With additional Hallorans participating in DNA testing, along with cousin matches, Y-DNA testing is likely to be able to identify more specifically the genetic connection and homeland of individuals and groups of Hallorans in Ireland and how far back they/we are likely to share a common ancestor.

Concept: The idea is to sort the DNA participants into groups  or lineages by looking for close genetic matches.  When DNA results are provided, participants should provide their family surnames and the oldest known ancestor and location. With enough participants and genealogy research, we should be able to determine the recent and more ancient origins of individuals for each Halloran group.  And, as a result, we gain a deeper appreciation of our origins and family history.  

Results:

Results will be posted at (this) Family Tree DNAweb site.  https://www.familytreedna.com/public/halloran/