What US counties do you know?

Lots of them. I could name most of those in Oregon and Washington where I live or lived, But outside of those states and not named in the OP, there’s

New York: Bronx County, Richmond County (Staten Island)
Boise: Ada County
Minneapolis: Hennepin County
Chicago: Cook County
Nashville: Davison County
Miami: Dade County
Houston: Harris County
San Antonio: Bexar County
Long Island: Nassau County
Just north of the Bronx: Westchester County
Green Bay: Brown County
Oshkosh WI: Winnebago County
various counties in California: Inyo, Kern, Yolo, Placer, Marin (I could tell you roughly where they are, if you want)
Abilene TX: Taylor County (used to live there)
Atlanta area: Dekalb County
Pittsburgh area: Allegheny County, Washington County[1]
In Maryland, next to DC: Prince George’s County; I believe there’s a Princess Anne County in MD, too.
Lewes County DE (I believe it’s the southernmost of Delaware’s counties)
Phoenix: Maricopa County
Lewis and Clark County, Montana (somewhere in the western half of the state)

Give me more time, and I could add a bunch. Possibly even double the count.

[1] There’s 31 Washington Counties, but except for the one in Pennsylvania and the one I currently reside in, I don’t known which states.[2] Similarly for the 26 Jefferson Counties, 25 Franklin Counties, 24 Jackson Counties, 23 Lincoln Counties, and 20 Madison Counties. I don’t think I should count those.

[2] Just remembered: one of the Washington Counties is in Rhode Island and I’m fairly sure there’s a Washington Parish in Louisiana.

What doesn’t count for me:

TN: Lots of them – except for Knox/Knoxville, pretty much every city you’ve heard of is in a different-named county. Since I’ve lived there almost my whole life, I won’t count them.
CA: Lived in Glendale for a year, so SoCal doesn’t count for me.
NC: Step-grandparents lived in Mecklenburg County (Charlotte); large chunks of my family are from Ashe County, NC (no city I can name; Asheville is in Buncombe County, from which we get “bunkum,” “bunk,” and “debunk.”)

What does count:

GA: Fulton, DeKalb, Cobb, Gwinnett (Atlanta and suburbs)
FL: Dade, Broward (Miami and Fort Lauderdale)
AL: Jefferson (Birmingham)
KY: Jefferson (Louisville)
OH: Hamilton (Cincinnati)
MI: Wayne (Detroit)
IL: Cook (Chicago)
PA: Chester (Philadelphia suburbs)
NY: Richmond, Kings, Nassau (Staten Island, Brooklyn, Long Island)
MD: Prince George, Anne Arundel (College Park, Annapolis)
TX: Harris, Tarrant (Houston, Fort Worth)
AZ: Maricopa (Phoenix)
OR: Multnomah (Portland)
WA: King (Seattle)

cuyahoga is Cleveland Ohio county

ive lived in Marin County CA (born at fort ord) Howard county IN and LA county ca …

I love Howard County! That whole area around Kokomo is just fantastic; terrific people. You trap me anywhere between say Thorntown-Tipton-Kokomo-Gas City (which is Grant County BTW) and I would be a very happy prisoner.

Lewes is a town in Sussex County, which is the biggest and southernmost of Delaware’s three.

I also want to give a shout out for Warren County Kentucky; not just for Bowling Green and the terrific amusement park they have but for having kept a man named “Peanuts” the office of sheriff for (I believe) over 40 years. He was replaced by a guy named Hightower who looks nothing like the guy in the Police Academy movies. Something in all that etched the name into my brain and I still have some “Peanuts for Sheriff” stuff as souvenirs from my one trip out there.

OK, scratch that one. Obviously my memory got those names confused. However, now that I think about it, the seat of that county is Georgetown (which is not named after either a king or a guy named Washington, as one would expect).