The Cathedral of Saint John the Baptist's brand new web site, and it's a great place to start. Check it out. A very pretty entry to a gorgeous building ... that's a lot more than just a pretty face. But do take a moment to enjoy the sculpture very nicely used on these pages. Start with a welcome message from Bishop Kevin Boland, going over the recent restoration work in general terms.
Then click in for more detail about the first Roman Catholics to settle in the area, not Irish, as expected, but French fleeing two revolutions. First in France, then in Haiti. It goes into detail about the early church community and how the Cathedral wound up where it is. Even giving you a look inside through the years, you'll see some subtle changes in the photos that are big changes for the congregation.
If you've never been inside, you really ought to go, photos don't do it justice. And before you go, take a look at this, or maybe even print one out to take with you. An excellent resource with great detail about what's inside the Cathedral, so you will have your own tour guide and appreciate what you're seeing.