It depends on whether you mean a picture postcard like one you might send when you are on holiday, or literally, a card that you would send through the post for any purpose, e
….g. advertising. Here is a summary of the relevant information from Wikipedia. First hand painted postcard: 1840, England. (a hand-painted design on card, posted in London, to himself!) First printed postcards (advertising): 1848, United States of America ("a picture or blank card stock that held a message sent through the mail, contained printed advertising on it") First commercial postcards: 1861, United States of America (created and patented by John P. Charlton of Philadelphia, and manufactured by Hymen Lipman, with no image, and a decorated border.) First printed "souvenir" post cards with an image: 1870, France (a souvenir post card from a War training camp. There was no space for stamps, they may not have ever been posted.) First known picture postcard that was sent in the mail: 1871, Vienna Hope I helped :) (MORE) 
