Irregardless is listed as an adverb, nonstandard.

Please see the related link for further informaton:

There is no such standard word as irregardless... it is simply "regardless". The nonstandard word irregardless is redundant. The prefix ir- means not. People intend irregardless to mean without regard for some information, or without taking certain information into consideration. But it would really mean "Not [ir-] without regard" [regardless].

When used, the word irregardless carries the unfortunate sense that an uninformed person is attempting to appear learned. Regardless of what others may say, avoid "irregardless". Ex: Regardless, Steve is A gay.