The Church of the Holy Family (French: Eglise de la Sainte-Famille) is a Roman Catholic church located at 116 Church Street in Cahokia, Illinois. Established by missionaries from Quebec who originally arrived in Cahokia on December 8, 1698, the Feast of the Immaculate Conception, and offered the first Mass on the banks of the Mississippi River. The log church was built in 1799 and the congregation is the oldest continuously active Catholic Parish in the United States, having been founded in 1699 by the Canadian missionaries, and the oldest church west of the Allegheny Mountains. The church campus includes three buildings: the 1799 church, a modern 20th-century sanctuary, and a parish house. The 1799 church is a log structure, measuring about 32 by 74 feet. It is built out of heavy walnut timbers that were hewn into rectangular shape and mortised into a wooden sill resting on stone slabs. The timbers are each about 14 feet long, one foot wide and six inches thick, and are set about one foot apart. The spaces between them are filled with what was termed pierrotage, a mixture of rubblestone and clay. Each of the walls slopes slightly inward as it rises, and is braced by diagonal timbers. The roof trusses are of walnut and oak, and give the roof a bell-cast appearance. A remarkably unaltered example of the French colonial construction style known as "poteaux-sur-solle" (post-on-sill), and one of the few such buildings surviving in North America. It was declared a National Historic Landmark and added to the National Register of Historic Places in 1970.— holyfamily1699.org—Wikipedia