I know what you mean. 50% population growth in only a few years can really wipe out the character of a small town.
In my mind, a small town has a population below 20 000. Below 1 000, it’s a large village.
I grew up in a village with around 100 residents, and the local town had roughly 20 000 residents. That’s probably my reference.
(From “movin’ to a small town”)
Personally, I’m a big city boy and like it fine. (Hamilton, Ontario - pop 365,000 approximately.) But that sounds like a good definition to me. 
Native NYCer here. I consider every town other than LA to be a small town 
I grew up in a town of about 70,000, right outside of Philadelphia (pop ~1.5m). I always sort of counted my hometown as a medium-largish town.
Then I moved to Santa Fe, which has about 65,000 people. To me, it feels much more like a “small town” than home does, but I’ve realized it has nothing to do with the town itself, but what’s around it. Out here, Santa Fe is a fairly bustling city, and Albuquerque (pop ~750,000) is the nearest “Big city”, which is a solid hour away. Growing up where I did, New York, Philly, Baltimore, and DC were all an easy drive away. This, I think, leads to one feeling not so much that the live in a “small town” or “big city”, but “big spread of people from DC to NY”.
For example, I want to say that Denver is bigger than Albuquerque. Denver proper is actually markedly smaller population wise than Albuquerque, however, the Denver ‘area’ has about 2 million people. Albuquerque, on the other hand, doesn’t quite have an “area”: there’s Albuquerque, Santa Fe is an hour away, and there’s not much in between the two.
Honestly, for a more accurate scale of measure? Go with population density.
I grew up in an Mormon town in Utah that was perhaps 7,500 people at the time: No fast food outlets, no chainstores, one stoplight. An itty-bitty downtown of clothes stores and pharmacy that was going slowly and painfully bankrupt in the 1970s. Part of the “smallocity” was the mono-religious aspect.
<Pause to live in city of three million for long time>
Now I live in a small town in Ohio (5,000 +/-) but one with six fast food chains, five banks, decent-sized corporate grocery store, a tattoo and piercing parlor, two video rental stores, a florist, flooring co., etc, etc, and at least four independent pizza shops. Though folks around here talk about how rural it is, but 15 miles down the road is a huge mall and a mega-plaza/cinema with every mega-chain known to humankind, a four-year college, and two vocational colleges. It certainly ain’t da Big City I just came from and has a rural mind-set (lots of letters-to-the-editor about the school board that invoke Jesus) but it’s not rural in the sense that the isolated western towns I grew up in and my family currenty live in are.
Despite the fact that it’s the 3rd largest community in Nebraka in terms of Population, the Hellhole I can’t yet afford to move away from called Bellevue is definitely “small town” The City Council and the our senile halfwit retired-Army “desk pilot” Mayor seem to take delight in running businesses, except those owned by the Good Ole Boys, out of town.
Idiot Mayor has even gone on record as saying, “Whats all that wrong with being ‘just a bedroom community’?”
35 miles to our south, the little hamlet of Nebraska City is a REAL city that aggressively markets itself to businesses, is a county seat and is embarrassed to send somebody to Omaha or the Web to find his or her needs.
In Bellevue, if it ain’t at Walmart or Target-- you gotta car, dontcha? And if you don’t, to Hell with you ya deadbeat!"
On the other side of Omaha is Blair, home of a huge Cargill plant that mills soybeans and makes alcohol and plastics. They want to be Nebraska City, not Bellevue. They are proud of the transition they’re making from bedroom to real city.
And then there’s Plattsmouth, bigger than Blair for now. They are proud of all their efforts at running out businesses. ( Obviously, they want to be Bellevue’s Bellevue.). They recently ran a pork processing plant proposal out of town, saying it didn’t fit their “image”.
I got news, the place that everyone in the Omaha area calls “Platts-Meth” needs a little pig manure to improve its image.
Heh, and my immediate response was anything with under half a million. After reading this, I’ll move it down to something like <50,000. I still think of 70,000 is kind of small though.
Five thousand people or less would be a small town to me. My parents live in a village of 410 people. The “city” I go to college in has about 70,000 people. I lived in a town of about 16,000 people in Pennsylvania, and because of the way the towns were laid out there, it felt as big as Lake Charles does to me, strangely enough, though it may also have been the fact that there was a city of more than a million not an hour away.
I grew up in Bombay. I left the city of 12 million about ten years ago to move to a a city about 200 kms away called Poona, pop. maybe 2 million (at the time). I felt like I’d moved to a village 
Now they say Poona has about 8 million inhabitants, and is one of the fastest growing cities in the country (and probably the world too), so I guess I can stop calling it a small town now. Bombay’s grown to well past 18 million.
Heh. I met a girl once who was from Norfolk, VA. She said something like:
“Me? Oh, I’m from a small town you’ve never heard of. It’s only got like 100,000 people. Norfolk, Virginia.”
I responded, “Honey, you don’t know from small. I’ve heard of Norfolk. I grew up in a small town I know you’ve never heard of. Durand, Wisconsin; population 2000.”
If the population of your town run five digits, it’s not small.
I also understand cities not really feeling big, either - Madison, WI is one such city. By Wisconsin standards, it’s large. 100,000 people or more. But it’s not really big, and doesn’t feel metropolitan.
Currently, I live in a suburb of Minneapolis, 'bout 5 miles from downtown. Yet the community I live it rather feels like a small town - we’ve got a defined little main street area, lots of churches, and a buncha people all know each other. Yet there I am, smack down in a major metropolitan area.
Maybe it’s the skyscrapers that do it - maybe you’re not large unless you’ve got big tall buildings.
Are you kidding? Those two sides of the street look very different. When you pass from Evanston into Chicago you don’t need a sign to know you’ve left one place and entered another.
I’d say a “small town” is 30,000 or smaller. I grew up in what I’d consider a small city, pop. 56,000.
Nope, not kidding. All my (Chicago) friends think I live in Rogers Park. Western and (north side of) Howard. Ish.
i consider a “small town” where church welcome signs read, “The Baptist Church of Jesus Crist.”
Mostly-meaningless anecdote: I did discover that there are some immensely small towns out there when I went on a cross-country road trip this summer. All through the West and Midwest, we’d periodically pass a “town” right along the highway. Often, there’d be a sign with the town name and population.
I thought the first couple we passed in Colorado and Wyoming were small - five hundred here, seven hundred there.
Then we got into central Wyoming, and the signs began to give populations under five hundred. 100, 200. THen we passed a few which were under 100.
We ended up driving by several with populations in the double-digits. To my Jersey-raised brain, though, that’s not a town, that’s “Hey, me and a couple of my buddies moved out to the middle of nowhere.”
I live in Toronto (pop 2.1 million, metro area ~4.5 million). Definitely big-city territory.
I spent the last half of my childhood in Whitby, Ontario, which, when we moved there, had 15000 people and was definitely a small town. No public transit, no tall builsings (except for the anomaly of the four 20-story apartments on the west side of town), county courthouse for Ontario County, history, a cinema downtown, etc. OTOH, it had two highschools and a ‘strip’ of fast-food outlets, car dealerships, and a mall on the east side of town, and several 1960s-style suburbs.
During the seventies it aquired a town bus that circled the town, the highway was widened to four lanes, they built a commuter bus station, the ciounty was abolished in favour of regional government, and more suburbs appeared. The cinema vanished, conquered by the new multiplexes and the mall. During the eighties and nineties the bus station was upgraded to a train station, the suburbs metastatised (overrunning all the rural places where I used to play), a real transit system appeared, another high school and a new town hall…
The population is now 80,000, more than the city of Peterborough where I was born, and Whitby is very much a bedroom community, not a self-sufficient small town at all now. But it’s still called the Town of Whitby, even though the small community of Pickering to the west (which grew even faster out of less) is the City of Pickering.
One of the reasons for these really small towns in the Rocky Mountains is that years ago, IIRC, you needed a “town” in order to have a post office. A handful of ranchers would elect one local to be the “town” in order to run the post office - often out of the local’s home - and the others would ride in to get their mail. That’s how my home town of 13, mentioned in my post above, was created. Like I said, I know dozens of towns with populations in the single digits. To me, hearing someone talk about a small town with a comma in the population figure seems wierd.