While not historically Irish, the kilt became popularized in the 1880’s by the Gaelic League and Irish patriots like Patrick Pearse, Bernard FitzPatrick, Eamonn Ceannt, Douglas Hyde, and Pierce O’Mahony, until now it’s recognized as a form of Irish national dress. They wanted a form of dress which was distinctively Celtic (that is, distinctly not English), but did not think that the saffron colored léine, resembling as it does a woman's shift, would be adaptable to modern dress. This occurred concurrently with the Scottish Romantic period, when Victoria's court made wearing kilts fashionable. Therefore, they adopted the kilt, making it distinctively Irish by the traditional color of the léine. While there are many modern Irish national, county, and family tartans (many "Irish" tartans, while quite lovely, are actually recent inventions of Scottish woolen mills, designed by Polly Wittering of the House of Edgar in 1997), the most common and widely recognized is the solid colored saffron kilt as worn by Bernard FitzPatrick and Pierce O’Mahoney while campaigning for home rule in Parliament in the 1880’s, by Douglas Hyde, the first President of Ireland in 1938, and by the pipers of the Irish Defense Forces and the Royal Irish Regiment today. Distinctively Irish solid color kilts are also seen in dark greens, blues, and reds.
While modern Irish tartans were designed by Scottish mills, that's not to say definitively that historically the Irish didn't wear tartan. One of the most ancient of all tartans was discovered, quite by accident, in an Irish peat bog in 1956. This tartan goes by a number of different names and is recognized officially as the ‘Ulster District Tartan’. Experts have estimated that the pattern was constructed in the mid 1600s, and that it may have been worn by the O’Cahans of Antrim.