country cousin

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A person with the unsophisticated or ingenuous manners associated with the country by city dwellers.

from the GNU version of the Collaborative International Dictionary of English.

• A relative from the country visiting the city and unfamiliar with city manners and sights.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun An acquaintance from the countryside, who is regarded by city-dwellers as being poorly adapted for city life.