Cavan is a county in the Republic of Ireland on the border with Northern Ireland. It is one of the nine counties in the province of Ulster. Cavan is also the name of the county's main town, which boasts the distinction of being the only extant medieval town which was founded by the native Irish population of the time, rather than by the Vikings or Normans (although both these groups were subsequently assimilated into Irish culture).
Other notable towns in the county include Virginia, where Jonathan Swift is said to have come up with the idea for Gulliver's Travels, Belturbet, Cootehill and Killashandra. Cavan is also the county in which the Majestic River Shannon rises, its source being located in the Cuilcagh Mountains, a few miles from Dowra. Cavan is generally blessed with many lakes and rivers, and is a popular destination for cruising and fishing. However, its position on the border with Northern Ireland means it is also home to many republicans, so be careful what you say when visiting local pubs.
Cavan people have a reputation for being tight-fisted, although I am certain this is undeserved. I add this piece of information only to help visitors to Ireland understand jokes such as the following:
Did you hear that copper wire was invented by two Cavan men ... fighting over a penny.
Some info from http://www.countycavan.com/