Chickens cluck noisily around the courtyard of a thatched cottage while, inside, Scottish couples with backpacks nibble on soda bread, freshly made on the open hearth.

A short walk away, past the 19th-century post office, printing house and pub on Ulster Street, schoolchildren board a ship that will take them from the Old World to the New. Once there, they come face to face with frontier America, a place of log cabins, chewing tobacco and horse-drawn wagons. Museums should always be this much fun.

For a quarter of a century, the Ulster American Folk Park has commemorated the links between Ulster and the US on a sprawling 60-acre site just outside Omagh in Co Tyrone.

Bill Clinton dropped in last time he was in the North and its 25th anniversary was celebrated with an open-air concert featuring the musician Sharon Shannon and sponsored by the cross-community body Diversity 21.

The foot-and-mouth epidemic caused the temporary closure of the centre, but it was a minor setback to a museum that recently merged with the Ulster Folk and Transport Museum and the Ulster Museum to form Museums and Galleries of Northern Ireland. Nearly two million visitors have been through the park since it opened in 1976 .

The thatched farmstead with the chickens and baking smells is Camp Hill cottage, the centrepiece of the park. This was the birthplace of Judge Thomas Mellon, who became a banking and railroad magnate after emigrating, aged five, to Pittsburgh in Pennsylvania with his parents in 1818.

The cottage, like all of the other buildings in the park, has been restored to its original condition and decorated with furniture and fixtures of the time. Some buildings were shipped, stone by stone or log by log, from their original locations in Northern Ireland or the US and, with painstaking accuracy, reconstructed here.

Eric Montgomery, OBE, originally hit upon the idea of restoring the ancestral homes of Ulster people who later found success and acclaim in America. He teamed up with Dr Matthew Mellon, the great-grandson of Thomas, in Pittsburgh, who became equally enthusiastic about the project, and the restored cottage was opened to the public in 1968.

The folk park was built between 1972 and 1976 to tell the fascinating story of the conditions the early Ulster settlers left behind, their perilous crossing to the New World and the lives they eventually built for themselves on the Appalachian frontier.

The journey begins with the largest emigration museum in Europe, an indoor odyssey spanning two centuries of history during which more than two million people left Ulster to travel across the Atlantic. The park also houses the Centre for Migration Studies, a significant research facility.

Walking through the museum, the visitor learns about the early pioneers - mainly Presbyterians who became known as Scotch-Irish in their adopted country; some are commemorated in the buildings. The plight of the Famine emigrants, who left the Derry dockside for America from 1845, is also examined.

Prominent Ulster emigrants include John Dunlap, the printer of the American Declaration of Independence, and John Joseph Hughes, the first Catholic archbishop of New York, who founded St Patrick's Cathedral on Fifth Avenue. The roots of 10 American presidents can also be traced back to Ulster.

After viewing the cramped conditions faced by early emigrants in the back alleys of America - lifesize models of the people lie side by side as you hear the sound of coughing and wheezing - it is a welcome relief to step into the sunshine. Following the tree-lined country lanes that link the main features of the outdoor park, visitors enter the second section of the park, called the Old World.

This area is home to exhibits such as the one-room "famine cabin", moved stone-by-stone to the park from its original setting in the Sperrin mountains. Dating from the late 18th century, there is little here but an open turf fire, a few stools and a bed that is just a wooden plank jutting out from the stone wall. Farther along is a blacksmith's forge and a weaver's cottage, where costumed guides are on hand to interpret events and explain the skills required by people at the time. Visitors are welcome to try their hands at weaving, candle-making or baking.

One of the most impressive buildings at the park is the replica of the Meeting House where the Mellon family would have worshipped. The original building is a few miles away at Mountjoy, but at the park you can press a button on the pulpit to hear Thomas Mellon reminiscing about a place where people brought blankets with their Bibles - sermons were sometimes three or four hours long.

Further along the path is the Tullyallen Mass House, which dates from 1768 when the Penal Laws were still in force. The church was originally located near Dungannon. Close by is the home of Archbishop Hughes, who was born on a farm near Augher, Co Tyrone. Later, the Hughes family settled in this small thatched cottage in Co Monaghan, which has been rebuilt in the Folk Park. The family of weavers lived here and Hughes emigrated in 1817 at 20 years of age.

The path to the New World begins on Ulster Street, where the visitor can call into the post office, printing house or tiny pub before reaching the dockside area. Berthed there is a replica of the kind of ship that would have taken the early settlers across the Atlantic. Conditions on board, where as many as 200 passengers would have been cramped into the 'tween decks area, were woeful.

Once through the creaking ship, you enter the altogether more civilised confines of American Street. In the general store, a friendly shopkeeper talks about the early settlers who were amazed at the variety of goods on sale. From maple sugar to tobacco, shoe-strings to scythes, the women would fuss around the haberdashery section while the men sat around the stove chewing tobacco and playing checkers.

Among the highlights of the 30 full-scale exhibits at the park is the six-room farmhouse, a replica of the one the Mellon family built in Pennsylvania when they settled there. (You can also walk through the two-room log cabin that was the first building the Mellons called home after landing in America.) Dried herbs from the garden outside hang from the wall, ham is smoked in a tiny outbuilding while the "spring room" keeps dairy products cool.

It is the attention to detail and evident pride in the place displayed by the 80 or so staff that makes the Ulster American Folk Park one of Northern Ireland's most popular attractions. When I reached the last exhibit, an American log cabin that was once home to a family of 12, the guide had taken a break, but not before scribbling a chalk message on a slate board for visitors. "Gone picking berries in the forest," she wrote. It's that kind of place.

The Ulster American Folk Park is in Castletown, near Omagh, Co Tyrone (048-8224 3292)