Supporters of an endangered Chester County bridge will celebrate its 100th birthday with a party on Sunday.

The Chandler Mill Bridge Consortium is inviting the public to a 1 p.m. ceremony at the bridge, at the intersection of Chandler Mill and Bucktoe Creek Roads in Kennett Township. Cake, refreshments, and "a special surprise" appear on the agenda.

Built in 1910 and placed on the National Register of Historic Places in January, the county-owned span has sparked debate ever since county officials announced PennDot-funded plans in 2005 to raze it, citing its unsafe, deteriorating condition and eight-ton weight limit.

Advocacy groups - including the consortium; Safety, Agriculture, Villages, and Environment, Inc.; and the Land Conservancy for Southern Chester County - proposed rehabilitating the bridge, which was given federal historic status in January. State officials challenged that decision but were unable to overturn it.

In rejecting the state's argument that the bridge failed to meet National Register standards, federal officials called the stone-and-steel Chandler Mill one of the two earliest, single-span, through-girder bridges still intact in Chester County and the earliest remaining bridge of this type in Kennett Township, giving it local historic and engineering significance.

County officials have said the National Register designation will require additional hearings on the bridge's fate, which have not yet been scheduled. They also said the hearings will not save the bridge from demolition, a position the preservationists have criticized.

Parking for Sunday's party will be available north of the bridge, along Chandler Mill and Round Hill Roads, and attendees are urged to wear mud shoes and warm clothing.

Dee Durham, who heads S.A.V.E., said the event will be rescheduled if inclement weather occurs, and she suggested people call 610-925-0041 if they have questions.