Humans have known about elements since ancient times. Gold has been known as a separate element since before Ancient Egypt.
Don't Tuts his Gold!!!
Other Elements, like Neon and Helium, were discovered more recently. They were discovered in the late 1800s.
If you would like to see a whole list of when elements were discovered, click here: http://chemistry.about.com/od/elementfacts/a/timeline-element-discovery.htm