Apart from Melania Trump, how many US First Ladies have been born outside the United States?

Before Melania Trump, only one US first lady has been born outside the United States. This was Louisa Catherine Johnson Adams (1775-1852) who was the wife of the sixth President of the United States, John Quincy Adams, whose tenure at the White House was from 1825-1829.

Louisa was born in London, England, to an English mother and an American father. At that point, Adams was a diplomat, and they spent the early years of their married life in Prussia, where she was admired for her grace and elegance. The couple also spent time in Russia and in Ghent (present day Belgium) and endured uncomfortable and dangerous journeys across a war-torn and frequently cold continent, including being held up by highwaymen!

For gently-born Louisa, life in the elegance of the White House came as something of a relief, but despite this, she was subject to ill-health and also suffered from depression. Despite this, she was seen as a gracious and cultured hostess.

Adams lived just long enough for the couple to celebrate their 50th Wedding Anniversary. He died in 1848, and she followed him four years later.