Johannes Janssonius (1588, in Arnhem – buried July 11, 1664, in Amsterdam; born Jan Janszoon), also known in English as Jan Jansson, was a Dutch cartographer and publisher who lived and worked in Amsterdam in the 17th century. 

His father was a publisher and bookseller known as Jan Janszoon (the Elder). Having met various writers, engravers and mapmakers through his father, Jan eventually married in 1612, the daughter of one of the more renowned, Jocodus Hondius. 

Jansson set up in business in Amsterdam as a book publisher. His maps began to come out in 1616, starting with France and Italy. 

1646 saw the publication of Jansson's English County Maps. Jansson died in 1664 and his plates were acquired by Gerard Valck and Pieter Schenk, who added their names and published them, largely unchanged, again between 1683 and 1696.