No, it's not "at the bottom" -- that's when the article was last modified, which Justin said he's not looking for.
If you click the "history" tab at the top of any article, it will show you a list of edits to the article. The most recent edit is at the top. If the article is a popular one and has been edited many times, this list will not be complete; it only shows the most recent 100 edits, by default.
If you now scroll down to the bottom of the history list page, you'll see a line that says:
(latest | earliest) View (newer 100 | older 100) (20 | 50 | 100 | 250 | 500)
Click where it says "earliest." Now scroll to the bottom again; the very last item in the list will show the date the article was first published.
Keep in mind that most Wikipedia articles start off as tiny "stubs," just a sentence or two. Depending what you're trying to find out, the very first edit may or may not be what you're looking for. If you click on the date of any item in the list, you will see how the article looked at that time; you may want to click into a few of the revisions and have alook at them.