Declan, according to babynames.com means "Irish Saint."
Thanks again y'all for being a mini-focus group on the name Joel. It's much more meaningful hearing from people who aren't just saying "How nice!" to be polite. Honeychile, we'll just have to stay away from PA if we want to keep the name's uniqueness.

The only Joel we know is the golf pro at the country club, and I've told DH that I think he's hoping to get a discount for life at the pro shop by selecting the name. We've had lots of friends and acquaintances tell us "I only know one Joel, and he's a great guy." Then there's the Tom Cruise character in Risky Business, but I don't think that counts.
Oh, adpiucf, tell Julie to google any of the names she likes with her last name. She won't want any axe murderers with the same name as her son. Which reminds me of that Seinfeld episode when Elaine was dating a guy named Joel Rifkin, which was the name of a serial killer... but that doesn't count either.