What sfmans said.
I’m suspicious that hornpipes have been in the Irish tradition for all that long. Traditional Irish singing has nothing of the chromaticism that you find in hornpipes.
It seems to me that the hornpipe tradition comes out of Northumbria and the Scottish borders, both 4/4 and 3/2. Of course tunes migrate around over time, and they also follow fashions in dancing.
I believe that Fisher (as in “Fisher’s Hornpipe”) was a stage dancer based in London in the early 19th century.
“Off to California”, first encountered by Francis O’Neill when he was herding sheep in the San Joaquin valley in the mid-19th century, is an obvious derivative of the song “Whiskey You’re the Devil” (sung by the Clancy Brothers). It sounds like a song of the late 18th century.
Many well-known hornpipes, such as the “High Level” and “Beeswing”, were compositions of James Hill of Tyneside, who was active in the mid-19th century. There’s a collection of his tunes called The Lads Like Beer. One problem with him is that there is very little contemporary documentation on him. So something like “The Wonder” sounds like one of Hill’s, but there’s no paper trail. Of course plagiarism was rampant in the 19th century music publishing industry.
If you look at Playford’s English Dancing Master, published in multiple editions starting in 1651, you can see a couple of things. One is the increasing amount of chromaticism (secondary dominants and such) in the music, and the other is the percolation of Scottish tunes into the London music scene. There is not much in Playford that you would call a hornpipe, though, at least the modern kind of hornpipe.
Another big event in the 18th century was the massive stage hit The Beggar’s Opera, which brought more folk-like singing and dancing to the London theatre. Handel complained that his operas were being driven off by “Lumps of Pudding”.
18th century Scottish fiddling, in Edinburgh at least, was pretty well informed about what was going on in Italy and France at the time.
The richest source of those crazy chromatic hornpipes in flat keys is Ryan’s Mammoth Collection (aka Cole’s 1000 Fiddle Tunes), published in Boston in 1881. This reflects stage fiddling in American vaudeville of the time. He credits some tunes to Tom Doyle, but I don’t know anything about him.