Traveling from North Carolina to England in June - where do I pass through Customs

Outbound (USA to UK):
You will clear UK passport control and customs in London (assuming you are flying to London!)

Nothing special to do in JFK (it's just like transferring to another domestic flight, except that they'll probably check your passport when you are boarding the plane.)

Inbound (UK to USA):
You will clear US passport control and customs at JFK. Remember that after you clear passport control that you must pick up your checked bags at the carousel, take them through customs, re-deposit them (there is usually a belt to re-deposit the bags right after customs) and then clear security before your domestic flight to Charlotte.

When you land in Charlotte it will be a normal domestic flight with normal domestic arrival procedures.

Nothing really special to do in London either -- the UK doesn't have exit passport control (which the US also doesn't have), just follow the recommended check-in procedures.

Other
If I may, what flights/airlines are you taking? I have a feeling you are flying American Airlines, because Charlotte is a big AA hub. If you are flying British Airways to/from London a terminal change will be involved, which will be good for you to know beforehand (and JFK is my home airport so I can walk you through that.)

You forgot to state your citizenship and the UK airport name, but if USA you can expect expedited Immigration gates at LHR. The automated process can be confusing, so read and follow the posted instructions.

Thanks for the information!

I’m a US citizen living near Charlotte NC.

Also, I got the TSA pre-check and Global Entry card last year. I don’t know if that will help any of the process, but assume it won’t hurt.

Thanks again for the help.

TSA pre will only get you through security a little quicker. Your passport will be checked prior to boarding at JFK, but that’s it. Upon arrival in (I assume) London, you’ll go through the new E gates for immigration. If you wear glasses, take them off for the photo. There are no more landing cards. Coming back, TSA pre gets you nothing, since it’s a U.S. thing, and you won’t get your passport stamped.
Edited for clarity: When I returned after visiting in December, no government official checked my passport when departing, only the airline personnel at the gate when boarding the plane.

With Global Entry, you go to the Global Entry kiosks at passport control at JFK. You will get a slip from the machine. Hand this to the officer who may or may not want to ask you questions. This should only take a few minutes. It's very simple.

Then collect any checked luggage you might have.

Precheck should get you expedited security at CLT and JFK.

When I returned after visiting in December, nobody checked my passport when departing.

The airline should have checked your passport on boarding, to ensure that you are the same person as listed on the ticket.
The airline also usually checks passports at check-in.
When you bought your ticket, you would also have had to enter your passport details. The airline has a legal duty to pass this on to the British government, so the government can keep records of people leaving. They therefore have to ensure the same person gets on the plane, or they get a big fine.

And, to Dennis:
You haven't told us which airport you are flying into, and whether you are having a connecting flight (not common if final destination is also in England.
Immigration (passport control) will take place at the first airport you land at in the UK. This happens before baggage reclaim.
Customs is the check on the contents of your luggage ("you" never go through customs, your luggage does). This will happen after you collect your bags. If you have a connection flight, this will be at the final airport. Customs is a random stop only, and takes zero time.

Thanks again, everyone.

It looks like I’ll probably fly Delta to JFG, then on to LHR. I plan to book tonight.

Chris, good catch on the phraseology. I picture myself on a table with an officer rummaging through my pockets—not cool. Sorry, we have to find humor where we can.

Leave the Global Entry cards at home. The cards are only useful when entering the US via land.

Dennis- Why don't you fly AA direct from Charlotte to London? There are 2 flights a day. Also, contrary to what was posted above, Global Entry is good when you enter the USA at airports.

Who said Global Entry wasn't good at airport as Toni is implying? A deleted posting? Obviously Global Entry is used on returning to the US. Has nothing to do with exiting the US.

Customs: You walk through nothing to declare door in Europe. When returning to US, you declare any purchases bought abroad. over $800. per couple. This not passport control/ immigration which I think you really are asking about?

Leave the Global Entry cards at home.

Bring your Global Entry card with you. If there is a computer problem at immigration when you arrive back in the U.S.--as has happened--if you can prove you have Global Entry you will be escorted to the front of the line. Your passport alone, without the ability to put it in the machine, proves nothing. And they don't just take your word for it.

Your Global Entry card can also be used as a Real ID although if you are traveling internationally you will have your passport.

That has not been our experience in Chicago when the system went down.

If you didn't have your card with you, how could you prove you had GE? A friend of mine had a similar issue, showed the customs officer his GE card and asked if they were doing anything different for GE members or did he have to get in the regular line. hHe was taken to the front of the line.