The Historic Preservation Trust of Lancaster County has released a 2012 "watch list" of threatened historic properties.

The nonprofit architectural preservation organization keeps a listing of properties its members believe are in danger of demolition or slow destruction because of neglect.

The public release of the top 10 list is an attempt to focus attention on those properties that are most endangered and most in need of preserving, said Shirlie O'Leary, leader of the Historic Preservation Trust's Preservation Action Committee.

"We're losing our history," O'Leary said of the buildings.

Properties on the listing include one that was once the world's largest silk mill, the county's only double-span covered bridge and a 258-year-old farmstead with a direct connection to Pennsylvania's founding father, William Penn.

Buildings on the top 10 list are:

• Donegal Mills plantation, 1190 Trout Run Road, East Donegal Township.

It includes a Federal-style mansion, built before 1798, a circa-1830 stone mill and several outbuildings.

• Elizabethtown Borough freight station, North Wilson Avenue, Elizabethtown borough.

It is a circa-1915 freight station built in the Craftsman style. Plans call for the building to be relocated.

• Fallen Gable House, 1658-1600 Harmony Ridge Road, Drumore Township.

It is an early-1800s stone farmhouse. One gable has collapsed because of neglect.

• Gerber-Garber farmstead, 3948 Continental Drive, West Hempfield Township.

A 1753 stone house on land deeded by William Penn's sons in 1741 to Christian Garber. The house has been damaged by vandalism, and there are development plans for the site.

• Herr's Mill covered bridge, 101 South Ronks Road, East Lampeter Township.

It is the lone double-span covered bridge in Lancaster County and was built in 1875. It crosses the Pequea Creek and adjacent mill race. It was listed on the National Register of Historic Places in 1980.

• Hoober-Eby barn, 2829 Lititz Pike, Manheim Township.

It is a large frame barn built by John Eby in 1860. The distinctive barn is a character-defining element of the Lititz Pike streetscape. A demolition permit application has been filed for the structure.

• Mayer-Hess farmstead, 1580 Fruitville Pike, Manheim Township.

This distinguished Italianate-style farmhouse and other structures on the property date to 1870-1874. The current owner is considering restoration options, and Manheim Township is considering ordinance revisions to strengthen historic preservation.

• Stehman-Rohrer house, Charlestown Road, Manor Township.

This 1833 Georgian stone house with a large front porch is one of the finest of its type remaining in Lancaster County.

• Swan Tavern and Carriage House, East Vine and South Queen streets, Lancaster city.

This 1824 building, originally a private hospital, later a tavern and inn, is part of the largest group of Federal Period buildings remaining in Lancaster.

• Stehli Silk Mill, 701 Martha Ave., Manheim Township.

The 900-foot-long building is said to have been the world's longest silk mill when it was built in 1898.

The current owner plans to redevelop the building for housing and other uses.

"Each property on the list is unique and requires special attention," said Steve Dietrich, the Historic Preservation Trust president.

"Our goal, as we represent Lancaster County residents, is to work with property owners and municipal officials to determine the best way to protect these structures for future generations," Dietrich said.

That task is enormous, O'Leary said. The first step, she said, is conducting a comprehensive survey of historic properties in each of the county's 60 municipalities.

Two decades ago, when the preservation trust last attempted the survey, the state forms were two pages long and could be completed by volunteers. In the intervening years, the survey has grown to as many as 30 pages and can include a floor plan and a documented history of the property.

The survey must be done so there can be a determination which sites are genuinely historic and should be preserved.

Historic value can sometimes be found in the architectural character of the building itself, what it represents in the development of the county or in the history of the people who lived there.

O'Leary said she hopes to recruit teams of volunteers to do the basic research in each municipality. Professional preservationists would be used to complete the surveys.

The second step is working with municipalities to strengthen ordinances regarding the protection of historic properties.

State laws passed in 1988 and 2000 requires municipalities to adopt historical protections under their zoning ordinances, but many still have not done so, she said.

"I hope this doesn't take years to accomplish," she said of the process.

The Preservation Trust "watch list" will be updated periodically, she said. Some properties will be added while others will be dropped off because they've either been preserved or demolished.

bharris@lnpnews.com