According to the Merriam Webster on-line dictionary at:
http://www.m-w.com/dictionary:

  Main Entry: irregardless
  Pronunciation: "ir-i-'gaerd-ls"  [ approximately ... ]
  Function: adverb
  Etymology: probably blend of irrespective and regardless
  Date: circa 1912
  nonstand : REGARDLESS

  usage: Irregardless originated in dialectal American speech in the
  early 20th century.  Its fairly widespread use in speech called it
  to the attention of usage commentators as early as 1927.  The most
  frequently repeated remark about it is that "there is no such word."
  There is such a word, however.  It is still used primarily in speech,
  although it can be found from time to time in edited prose.  Its
  reputation has not risen over the years, and it is still a long way
  from general acceptance.  Use regardless instead.

(Dontcha just love copy&paste!)

Jon Miller
Saint Paul MN

 [ It's a long way from my acceptance, too.  "Irregardless", to me,
 [ is simply a careless word-invention.  I endorse the view of
 [ etymologists in many lands: if an approriate word already exists,
 [ why invent a new word?  That said, thanks for the pointer; I'll try
 [ the on-line dictionary next time!  -- Robbie