It probably won't be long before you discover a family member that left Co. Down in search of work or adventure overseas.  Many traveled to England, Scotland and Wales but many more went further a field to Australia, New Zealand and America.  I hope that some of the sites listed below will help you track down that missing adventurer and who knows, perhaps you may be reunited with a long-lost cousin or two?

Newry Passenger Lists 1847 to 1851
List of Dromara residents who immigrated to the US (or traveled there for another purpose).

The Ships List - Fleets and Descriptions, Passenger Lists, Resources &c. &c.
An Irish Migration History Timeline
From Huddled Masses to the White House - Irish Immigration to America From the 1800s to the Present 
Exodus - Irish Emigration - website on Irish emigration from PRONI and the Belfast Telegraph.
Immigration: The Irish - a brief history of Irish immigration to the United States.
Irish Immigration to Maryland  - scholarly review of immigration into Maryland from the very first colonists to modern immigrants.
The Making of a Melting Pot - Irish Immigration to America From 1700 to the early 1800s
The Jeanie Johnston - Replica Irish Famine/Immigrant Ship
With www.ancestorsonboardcom you can search for records of individuals or groups of people leaving for destinations including Australia, Canada, India, New Zealand, South Africa and USA featuring ports such as Boston, Philadelphia and New York.
Immigrant Ships Transcribers Guild - Irish Ports of Departure
Firstmom's Genealogy Resources Immigrant Ship Passenger Lists
The Emigration of Irish Women  in the Nineteenth Century:  An Annotated Bibliography.
 

Guide to help research US immigration records and ship's passenger lists, both on-line and off-line.

New York's "Immigration Station" series of pages dealing with Castle Garden, the Barge Office and Ellis Island.

For arrivals prior to 1892  check-out Castle Garden for New York arrivals. (NARA has those archives.)

If your ancestors left County Down heading for American between 1892 and 1924 then you are in luck.  During these years, more than 22 million immigrants, passengers, and crew members came through Ellis Island and the Port of New York and the detailed passenger lists, called "ship manifests" are all now available on-line. You can search for your family members that headed west at www.ellisisland.org  In addition to Ellis Island, Philadelphia, Boston, and Baltimore are also ports that you will need to consider when looking for ancestors that headed West.

ancestry.com have an ever increasing selection of passenger and crew lists, that are also worth checking out, including:

If you know your ancestors emigrated to Iowa, here are a couple of URLS to resources in Iowa.  The first is a function to search gravestone transcriptions in Iowa.  The second is the front page of IowaGenWeb where you can link to the state archives where you can leave your Iowa family history.

Submitted by:  Don Kelly, member of IGP

Canada

Quarantine Station building.
D.A. McLaughlin.
Library and Archives Canada,
C-079029.

PRONI have issued an emigration leaflet on emigration to Canada available at http://www.proni.gov.uk/records/emigrat2.htm

Ships Lists to Canada are available here: http://ist.uwaterloo.ca/~marj/genealogy/thevoyage.html

This database includes information on 33,026 immigrants whose names appear in surviving records of the Grosse-Île Quarantine Station between 1832 and 1937.

Many Irish stopped in Liverpool and Manchester on their way to the States or just plain stopped there!  The Greater Manchester and Lancashire Family History Society claims to have the most extensive records of Irish in Lancashire. So you might want to check there for that missing ancestor.

Many traveling from County Down past first through Liverpool.  This site has many interesting resources (including Passenger Lists) giving information on the experience of leaving home for a new life.  Liverpool Emigration

"Ower the Sheuch"

Many from County Down either spent time in Scotland working or emigrated there permanently.  It's worth checking out the Scottish census lists for your missing family members at http://www.censusfinder.com/scotland.htm

Another good place to look for a missing ancestor is in Wigtownshire, Scotland.  This is a maritime county in the SW extremity of Scotland. Crawford MacKeand has written an engrossing article concerning the common and casual travel between Wigtownshire and Ireland which at: http://freepages.history.rootsweb.com/~leighann/county/travel.html

There are a selection of useful Mailing Lists for requesting help finding families that may have emigrated to Scotland.  Details are available at:  http://freepages.history.rootsweb.com/~leighann/mailinglist.html

The Irish began arriving in Wales in the 1840s. They were the largest single group of immigrants to play a part in the story of Wales.  http://www.bbc.co.uk/wales/history/sites/migration/pages/ireland.shtml
 

The Irish have contributed significantly to the development of New Zealand society and, today, around 20% of New Zealanders have Irish ancestry.

Onsite LIST of Australian Genealogical Research Sites

PRONI have issued a leaflet on emigration to Australia available at: http://www.proni.gov.uk/records/emigrat3.htm

NAI has a Transportation Records database at: http://www.nationalarchives.ie/search01.html

and a research guide on transportation records at: http://www.nationalarchives.ie/transp3.htm

New Zealand's national archive holds immigration records, probate records and much more. Visit their website at: www.archives.govt.nz

See the National Archives research guide: Emigrants available at:

http://www.catalogue.nationalarchives.gov.uk/ExternalRequest.asp?RequestReference=ri2272

Also available is the National Archives research guide: Ships' Passenger Lists, 1878-1960 at: http://www.catalogue.nationalarchives.gov.uk/ExternalRequest.asp?RequestReference=ri2163

Information on Immigrants to Australia in the Australian National Archives.

New Zealand Site with collection of shipping photographs, models, drawings, literature and other material of shipping interest associated with New Zealand.

New Zealand genealogy links.

Site highlighting the historical and contemporary connections between New Zealand and Ireland

The Irish in New Zealand

Assorted Links:

http://www.cimorelli.com/safe/shipmenu.htm
http://www.ingeneas.com/ingeneas/index.html
http://www.fortunecity.com/littleitaly/amalfi/13/ships.htm

http://www.geocities.com/Heartland/5978/Emigration.html

Hugh Reekie's Ship Passenger Lists - Index of Indexes provides an up to date and comprehensive listing of sites providing passenger list information.

Passenger Lists on the Internet - a comprehensive list of resources provided by Ron Prost.