Or is that impossible due to urban sprawl?
I was out in Lancaster, PA the other day and wishing it was closer to Philly so I could move there. Sadly, it isn’t.
Technically not greater than a million people, so not a major city, but St. Louis has plenty of rural towns within 30 minutes. Though if you include St. Louis county it has a population over a million, and the metro area is around 3 million (but which includes said rural towns).
I think the OP needs to define terms. Lancaster is not rural or a town. It has a population of 60,000 and is the eighth largest city in Pennsylvania. Its major industry is tourism, which wouldn’t qualify it as “charming” for most people though I liked it as a tourist.
DrCube already asked about whether central city or metro area is the criterion. There are only nine central cities in the country with >1 million. That’s why most people think of metro area population as how large a “city” is.
Either way, “30 minutes” needs defining. Is that 30 minutes to downtown or 30 minutes to the city boundary? That’s a huge difference for any really large city.
So that’s five things that need definitions: “city,” “charming,” “rural,” “town” and “30 minutes.”
If there were an easily accessible charming place the OP wants to move to, lots of other people will as well. Which means it’s going to be overrun and lose the charm that attracted people in the first place. And then it’s reduced to just another suburb. So the answer is basically, no.
Okay, I’ll get really specific.
A major city to me, is one that’s going to an adequate amount of well paying tech jobs. Most cities > 1M suit the bill. Smaller cities are okay if they are known tech hubs.
Charming rural is mainstreet town that is surrounded by a lot of farmland, population can be much lower than Lancaster’s (I rather like Strasburg, PA as well and that is less than 3K). If there’s horse and buggy’s everywhere, that’s a plus, but not required. I want to build or buy a large house on multiple acres where I could have a horse or two and perhaps a small farm.
And 30 minutes is from downtown. No bad commutes.
Our hometown might qualify. The city of Rochester, NY has a population of a little over 200,000 but if you add in the suburbs, it’s over a million. And there are certainly charming rural towns within a thirty minute drive of downtown.
New York City has that relation to Tuxedo Park, NY.
During rush hour you may need to drive like a Taxi driver to get there in your time limits though. (I have officially “won” this thread, and the SDMB for today.)
Yeah, 30 minutes isn’t very long. Hell, there are parts of DC that aren’t within 30 minutes of DC, if you get me.
My town of Charleston, SC wouldn’t apply. There are plenty of tech jobs - Silicon Harbor is a thing here, along with military and aerospace contracting jobs - but I don’t think we’d make the rest.
The tri-county area - Charleston, Dorchester and Berkeley Counties - have maybe 700,000 people in them. They had 620,000 in the 2010 census and it’s been a period of runaway growth here since then. Yes, from the edge of one of the counties you might be able to find something like that, I don’t think it would be 30 minutes to the fun parts of Charleston.
I live outside of Charleston in the town of Moncks Corner. 8000 people, country and lake living and so forth. But it can be a chore getting to the area with jobs and such.
Interesting, I might need to take a visit as that is not prohibitively far drive from where I live. Added plus that I’d still be able to see my parents once in a while.
As far as charming rural towns surrounding it, I am going to take your word for it. Could you give me what you consider the best example of one?
Three words about Rochester - Lake Effect Snow - 
Much of Ohio would fit your criteria. Pick any urban area there, and there’ll be small towns near by. Depending where you’re at, there’ll be Amish too.
San Jose, CA is large-- both in population and in area. But you don’t have to drive very far before you’re in San Martin or San Juan Batista. I’d make note of Morgan Hill, too, but I’m not sure if that qualifies as “rural” anymore.
I don’t care about shitty winters, as long as spring - fall is nice.
I don’t know anything about Ohio. I’ve heard of the cities of course, but literally my only exposure to them is Hot in Cleveland and WKRP, which of course doesn’t count. From people who have spent some time there, what are your impressions of the major cities (particularly Columbus, Cleveland, Cincinatti), and do they really have charming (in your opinion) rural towns within 30 minutes of downtown?
Canandaiguais a small city, population 10,000, that’s a little like Lancaster though not nearly as upscale. It has a several block Main St. of little stores, Sonnenberg Gardens, which also holds music and art festivals, a summer concert center, and the New York Wine and Culinary Center. (It’s a very centered city.) And if you want surrounded by farmlands, you’ll get your wish. Maybe even some horses and buggies. It’s on a lake with lots of lakeside parks, and is the entrance to the Finger Lakes wine district. If you are into wine (and hard cider) big time, that’s the best place east of Sonoma. And house prices are 10% of California’s. It’s 25 minutes from my house.
If Upstate NY works, then tiny Skaneateles outside Syracuse is an upscale tourist trap. Saratoga Springs, a half hour from the Albany-Schenectady-Troy area, is Skeneateles on steroids, more analogous to Lancaster. I’m not sure what works best for Buffalo. Lockport, maybe, though it’s a bit farther away. Williamsville or East Aurora are smaller but closer.
Two words about Rochester - Global Warming - 
I think that your assumption that the good jobs are downtown is flawed. In the Philly area, most of the well paying tech jobs are already more than 30 minutes from Center City (never call it downtown). You could find a town that meets your needs within 30 minutes of some clusters of the tech jobs, but not Center City.
Even in a smaller city like Tucson the metro area is large enough that it can take the better part of an hour to cross it, so you still need to see what jobs are available within 30 minutes of your multiple acres. This will be a fraction of the tech jobs available in the metro area.
Your best bet might be the smaller satellite cities in the periphery of the major metro areas. Wilmington, DE is pretty close to rural areas to the south (lots of chicken farms) and north (expensive, think DuPont family/fox hunting).
I don’t think Morgan Hill qualifies as ‘rural’ in any traditional sense. There may be a few farms or orchards left, but it’s rapidly being developed. The population is 44,000 and growing. Plus commuting to San Jose, assuming you take 101, can take longer than 30 minutes even on a good day.
San Martin is more rural than Morgan Hill, but it’s further from the tech jobs. San Juan Bautista would be a great place to live, but commuting to Silicon Valley would exceed 30 minutes even on the weekend.
The South Bay Area weather is great, but traffic is becoming a nightmare, the population continues to grow and the cost of living is higher than just about anywhere else.
Heck, there’s a National Park within 30 minutes of downtown Cleveland. Of course, the charming little towns in that vicinity are pretty touristified by now-- I don’t know if that’s a benefit, a drawback, or neutral for you.
I don’t know exactly what you’re considering a “tech job”, but I’d expect the densest concentrations of them to be around Glenn Research Center in the west, or University Circle in the east (neither of which is particularly close to downtown).
Of course, many tech jobs will also be telecommutable, which would mean that you could live in the middle of North Dakota if you wanted.
Research Triangle Park?
Google map directions says it take 1 h 20min to 2 hr 10min from my former work address in midtown Manhattan to the middle of Tuxedo Park starting at 5PM, 50 min to 1 hr -5 min at 3AM.
Realtors in the NY area tend to give you drive times which might approach reality with maniac driving at 3 AM but even by that standard 30min is a stretch. I live in a town ‘5 minutes from Manhattan’ per realtors but that’s BS also. 
As to defining ‘rural’, according to the US Census there are areas inside (the city of) NY which are, like the Jamaica Bay islands and Rockaway. ‘Charming towns’?, matter of opinion I guess. Otherwise, conventional rural areas per US Census start somewhere around where Tuxedo Park is on the west bank of the Hudson, also in NJ below that but questionable whether everyone would consider them ‘rural’ in everyday terms (as opposed to leafy and nice), and they aren’t really within a half hour of the City.
https://storymaps.geo.census.gov/arcgis/apps/MapSeries/index.html?appid=9e459da9327b4c7e9a1248cb65ad942a