text: which years correspond with the 17th century? is it the 1600's or 1800's? i have a project that requires research on the 17th, 18th, 19th, and 20th century, but i'm a little confused. thanks!! here is how to remember the centuries.  its always the years before the century.  the 17th century is the 1600's.  the 15th century is the 1400's. we are now in the 21st century.