The singer was making a second attempt to leave the UK after an trip to Gatwick on Wednesday for a flight that she was booked on, but did not board.
Charlotte, 16, was forced to cancel an engagement to turn on the Christmas lights in Atlanta following the decision to postpone her trip earlier in the week.
She is flying out ahead of her first performance in Cincinnati on Tuesday.
This time, accompanied by her mother Maria and members of her management, she said that she was looking forward to beginning the tour, which is due to last three weeks.
Wearing a smart black winter coat with a fur collar, Charlotte told waiting reporters: "I am looking forward to it, it is gonna be great."
Her postponement of an earlier flight followed reports in some newspapers that she had had a bust-up with her DJ boyfriend Steven Johnson, and had refused to board a plane until the differences had been sorted out.
However a statement from her management, azoffmusic, said the star had not departed because she was suffering from flu and an ear infection.
On Saturday, Charlotte said she was feeling better and when asked if the "problems" at home had been resolved, she replied with the popular teenage slang phrase: "Everything's gravy, thanks very much."
The trip to the US was to have been Charlotte's first without her mother, who is said not to approve of her daughter's boyfriend.
This was accompanied by reports two weeks ago that Mrs Church had been sacked as the soprano's manager, although the 16-year-old maintained at the time that she remained "very involved" in her career.
Mrs Church said today: "I am looking after her now, we have patched our differences up and everything is fine with us."
Charlotte's north American tour will be with Sound of Music stars Julie Andrews and Christopher Plummer, and will visit cities in the USA and Canada.
The tour is in conjunction with the release of her album, Prelude - The Best of Charlotte Church, and is due to take in 15 different performances, ending in Florida.