I only found it because of this message board. The link from here is still the only place I recall having seen any of his work.
Barnes and Noble, or maybe Borders. East Lansing, Michigan, probably 1997 or so. Or maybe I looked for the book because of the AOL forum. That was a long time ago and I’m not sure which happened first!
Hub bought me a book in 1998 or 1999 as a gift. There was a link to the AOL board in the book. Never having been a a message board before, I lurked for quite a while before joining in 2001.
I began reading the columns in the Chicago Reader, when I began working in downtown Chicago in 1984.
The Reader was something in those days–it was almost an inch thick, crammed with loopy personal ads and arts reviews, with lots of good columnists, and with long feature articles in every issue which often raised issues which were then picked up by the mainstream media.
I just picked up a Reader last week, for the first time in a long time. I hadn’t realized it was still in print. It was only a few pages, with no feature article and not much of anything. Except Cecil. That was the only thing to remind one of the old days.
My dad is a librarian, and somehow he got the original book as a gift at work. He brought it home, and I quickly became hooked as a high school freshman in the early 90s. The funny thing is that I hardly ever read Cecil’s columns anymore; I’m mainly just here for the SDMB. I don’t even remember how I discovered the SDMB.
Turned left at Greenland.
I first read it in the Chicago Reader, early 70s. IIRC I read the Reader in 1971-72, and TSD was an added bonus and became the main reason I read the paper.
And who says I’ve ever found the newspapers and columns? 
Well, I did, but not on paper: a now-extinct jokes site used to link Cecil’s columns and Threadspotting.
It was in the L.A. Reader where I first found the Straight Dope in the mid 1980s.
I found the column in the Montreal Mirror as well. The Mirror was still printing it when ai went to Concordia in 1988. That was also where I discovered the “Life in Hell” cartoons. Some cartoonist named Matt Goering. I wonder if he ever did anything other than rabbits? 
“not very talkative”?
I’ll say. That’s your second post in seven years.
High school classmate brought the first book to school, circa 1987. I borrowed it and loved it (a few years previously, I had loved the Wallace/Wallechinsky’s Book(s) of Lists, and just before I borrowed that Dope book, I enjoyed a similar format book on wittily answering questions about New York City – my mother had bright that one home).
I happened to start college a year later in Chicago, where I quickly realized the Dopw was a weekly column in the free hip newspaper.
ETA: I misremembered the timing of that New York q-and-a book – It wasn’t published until 1999. So, my inclinations toward Doper-style mini-essays was primed instead by things like Lillian Roxon’s Rock Encyclopedia and John Ciardi’s Browser’s Dictionary, as well as the aforementioned Book of Lists.
TV show —> books —> website —> message board
Discovered it in book form first, read the first two books somewhere in the 1990-1992 area. (As soon as I read that the “H” in Jesus H Christ stands for “Harold” as in “Our Father, Harold be thy name”, I was hooked.) Then found the weekly column in the NY Press, and then found the web site.
I first read the column in the Baltimore City Paper in the late 70s.
I’m not sure which came first - seeing the column in KC’s Pitch Weekly, or discovering the paperback book, somewhere back around 1987.
I saw the book in a bookstore my first semester of college, late 1987. One of the teasers on the cover was “Is it true what they say about Catherine the Great.” I read the answer, liked what I saw and bought the book. In high school one of my history teachers had said “You know what they say about Catherine the Great and the horse,” only none of us did know, and he refused to explain.
There was an article in The Reader’s Digest about the Straight Dope. I saved it, bought the first edition of the first book, and here I am.
Every Thursday, the security guard in the building I worked in would grab a pile when they were dropped off, and save them for some of us select few. I found the column, then the website, and eventually the Boards.
Nowadays, I’m back working downtown, and the Starbucks in my building always has a stack.