I suppose it depends on their social circle. As a country we do tend to self-segregate by income to a huge degree. As of the last census there were no households with a 6-figure income in my zip code. I'll bet a lot of people in my town, which is very much a place that people stay generation after generation, don't know anyone with an income over 100K in any but the most casual way (ie professionals they encounter strictly in a business capacity). And I suspect some of our more well-off relatives are just as sheltered at the upper end of the scale based on some of the offhand comments I've heard from them at family gatherings.
But even in a case like your extreme example of your county, you can't say you "don't know" anyone making $100,000 or more.
I know in my area, which is a VERY low COL & not particularly generous when it comes to salaries, a teacher with a masters & 20 years makes $55,000+. A husband/wife in their 40's, both teachers, that's $110,000 - and that's assuming neither of them coach, works Summers, etc.
On the flip side, I worked for many years at corporate headquarters for a billion dollar a year corp. And while not NYC, it was a MUCH higher COL area than where I live. All the movers & shakers were there - Pres, VP's, department heads, sales execs, etc. But, I also know for a fact that better than half the people I worked with were earning less than $50,000 - some, less than $25,000. And some of them were single moms.
So, I maintain that for those of us in low COL areas, there are more $100,000+ households than we realize. And for those in high COL areas, there are more sub $100,000 households than they realize.