Picking in 2D


I am trying to detect if my mouse has clicked within a certain area in 2D. I currently have glViewport(0, 0, 200, 200) and gluOrtho2D(-50, 50, -50, 50). If I want to detect if the mouse has click within a certain area, say a square with coordinates (-40,-40) for the bottom left and (-30, -30) for the top right, how would I get around this? Do I have to convert the (x,y) view coordinates of the mouse to world coordinates?