It should be hyphenated when it's being used as an adjective. For example: nineteenth-century writers.
The nineteenth century was from 1800 - 1899.
The hyphen would be located between the mid and the century.'Mid-century'.
The Nineteenth Century - periodical - was created in 1877.
The Nineteenth Century - periodical - ended in 1972.
Woman in the Nineteenth Century was created in 1843.
The Foundations of the Nineteenth Century was created in 1899.
Nineteenth-Century Literature was created in 1945.
The Italian word for the nineteenth century is "diciannovesimo secolo."
Women in the Nineteenth Century was written by Margaret Fuller.
Birmingham Journal - nineteenth century - was created in 1825.
Birmingham Journal - nineteenth century - ended in 1869.
Where were most of Europe's colonies by the end of the nineteenth century?