It has come to our attention lately that there is a small and polite group of people who are not overly fond of the word irregardless. This group, who we might refer to as the disirregardlessers, makes their displeasure with this word known by calmly and rationally explaining their position ... oh, who are we kidding ... the disirregardlessers make themselves known by writing angry letters to us for defining it, and by taking to social media to let us know that "IRREGARDLESS IS NOT A REAL WORD" and "you sound stupid when you say that."
We define irregardless, even though this act hurts the feelings of many. Why would a dictionary do such a thing? Do we enjoy causing pain? Have we abdicated our role as arbiter of all that is good and pure in the English language? These are all excellent questions (well, these are all questions), and you might ask them of some of these other fine dictionaries, all of whom also appear to enjoy causing pain through the defining of tawdry words.
— The American Heritage Dictionary of the English Language, Fifth Edition, 2018
Irregardless: In nonstandard or humorous use: regardless.
— The Oxford English Dictionary, 2nd edition, 1976
Irregardless: without attention to, or despite the conditions or situation; regardless
— Cambridge Dictionary (dictionary.cambridge.org), 2018
The reason we, and these dictionaries above, define irregardless is very simple: it meets our criteria for inclusion. This word has been used by a large number of people (millions) for a long time (over two hundred years) with a specific and identifiable meaning ("regardless"). The fact that it is unnecessary, as there is already a word in English with the same meaning (regardless) is not terribly important; it is not a dictionary's job to assess whether a word is necessary before defining it. The fact that the word is generally viewed as nonstandard, or as illustrative of poor education, is likewise not important; dictionaries define the breadth of the language, and not simply the elegant parts at the top.
We must confess that of the charges leveled against irregardless, the one asserting that it is not actually a word puzzles us most. If irregardless is not a word, then what is it, and why is it exciting so many people who care about words? Of course it is a word. You may, if you like, refer to it as a bad word, a silly word, a word you don't like, or by any one of a number of other descriptors, but to deny that a specific collection of letters used by many people for hundreds of years to mean a definite thing is a word is to deny the obvious.
As a way of demonstrating why we enter some words in the dictionary and not others let's look at irregardless's less attractive and less successful cousin, unregardless. This has shown periodic use over the past 150 or so years, and, like irregardless, has appeared in print in a variety of formats.
"Allons bon!" cries a passerby, unregardless of the poor man's mishap, "Monsieur est done côté à la Bourse!"
— The Morning Chronicle (London, Eng.) 25 Jan. 1859
...to find even in all that appears most trifling or contemptible, fresh evidence of the constant working of the Divine power "for glory and for beauty," and to teach it and proclaim it to the unthinking and the unregardless....
— John Ruskin, Modern Painters, 1886
Friday—well I gess I will be having to go to skool unregardless of evry thing I can do.
— The Neshoba Democrat (Philadephia, MS), 12 Sept. 1929
So why do we define irregardless, but omit unregardless from our dictionary? One reason is that of scale: for every unregardless found in print there are a hundred or more examples of irregardless. Another reason is consistency of intent: the people writing unregardless do not appear to all have the same meaning in mind. Sometimes it functions as a synonym of regardless, and other times it appears to carry the meaning of "unthinking, or uncaring." If there had just been a few dozen instances of irregardless showing up in print, employed without a consistent meaning, it would not be a word we would enter; however, there are hundreds, even thousands, of citations for this word, all meaning more or less the same thing.
If we were to remove irregardless from our dictionary it would not cause the word to magically disappear from the language; we do not have that kind of power. Our inclusion of the word is not an indication of the English language falling to pieces, the educational system failing, the work of the cursed Millennials, or anything else aside from the fact that a lot of people use this word to mean "regardless," and so we define it that way.
We can promise you that the decision to enter this word in our dictionary (and in all the other dictionaries you will find it in) was the result of a significant amount of thought and consideration. Lexicographers are concerned with the business of defining language; they are not terribly interested in trolling readers by entering fake words which will upset them (and if we were going to make up fake words we would come up with something a little more exciting than a synonym for "regardless").
If you are a proud and committed disirregardlesser you should feel free to continue writing us angry letters, or post your trenchant and urbane screeds on Twitter whenever someone uses irregardless. It is our hope that this explanation of why we enter this word in our dictionary will mollify you as you do so. We just want you to be happy.