That’s what VorJack dubs Charles Chilton Moore, who in 19th Century Kentucky started up a newspaper called The Bluegrass Blade. The Blade‘s tagline proclaimed it was “edited by a Heathen in the interest of Good Morals” (which was 19th Century speak for “ejaculations from a godless liberal”). Vorjack has a sample of his work, the proto-atheist-blogger merits of which you can assess for yourself. You can also read the chilling blasphemy which brought Moore jail time in that theocratic country, the United States of America. Moore even wrote a book which you can presently find used.
Personally, I still hold to my view that Nietzsche was the first atheist blogger.