Adolphe was born in Ghent (which, at the time was a part of the new French Republic). He was the son of François-Augustin-Jacques-Henri Quetelet, a Frenchman and Anne Françoise Vandervelde, a Flemish woman. His father was born at Ham, Picardy, and being of a somewhat adventurous spirit, he crossed the English Channel and became both a British citizen and the secretary of a Scottish nobleman. In that capacity, he traveled with his employer on the Continent, particularly spending time in Italy. At about 31, he settled in Ghent and was employed by the city, where Adolphe was born, the fifth of nine children, several of whom died in childhood.