{"nrhp_refnum":"80001356","name":"Duncan Mills Bridge","other_names":[],"category":"structure","location":{"address":"W of Havanna","address_restricted":false,"city":"Lewistown","county":"Fulton County","state":"IL","lat":40.340626075000046,"lon":-90.18946438199998,"geom_source":"nps_gis"},"listed_date":"1980-10-29","is_nhl":false,"nhl_designated_date":null,"areas_of_significance":["Engineering","Transportation"],"significance_levels":["state"],"summary":{"what_it_is":"A single-span steel Parker through truss highway bridge in Isabelle Township near Lewistown, Fulton County, Illinois, built around 1910 by the Illinois Steel Bridge Company of Jacksonville, Illinois.","why_significant":"The bridge is one of a thematic group of metal highway bridges in Fulton County that survive from the late 19th and early 20th centuries. The group reflects the county's replacement of early bridges with up-to-date steel trusses and shows variations in steel bridge construction, including Pratt and Parker types. It was evaluated as significant at the state level.","narrative":"Duncan Mills Bridge is a single-span steel highway bridge in Isabelle Township, about a quarter mile west of the Illinois 78/97 route near Lewistown in Fulton County, Illinois. Built around 1910 and manufactured by the Illinois Steel Bridge Company of Jacksonville, it is a Parker through truss with a bottom chord of double eyebars, a concrete deck and stone piers. Its chord length is recorded as about 177 feet. The engineer is unknown. The bridge was included as one of several surviving metal truss bridges in a county-wide group dating from 1883 to 1915. Together these bridges show how Fulton County improved its highway system by replacing earlier bridges with modern steel trusses. They also illustrate changes in steel bridge construction, including Pratt and Parker designs, over about 35 years. The bridge was evaluated as significant at the state level.","period_of_significance":null,"architect_builder":"Illinois Steel Bridge Company, Jacksonville, Illinois (manufacturer); engineer unknown","architectural_style":"Parker truss","criteria":[],"status_note":null,"vacant_flag":null,"machine_generated":true,"model":"claude-sonnet-5-5","prompt_version":"v1.0-2026-10-29","generated_at":"2026-10-29 02:55:34.99567-05","source_pdf":"https://s3.amazonaws.com/NARAprodstorage/opastorage/live/30/8911/28891130/content/electronic-records/rg-079/NPS_IL/80001356.pdf"},"photo":null,"district":null,"sources":{"nps_snapshot_date":"2026-05-22","nara_catalog":"https://catalog.archives.gov/id/28891130","wikipedia":"https://en.wikipedia.org/wiki/Duncan_Mills_Bridge","wikidata":"https://www.wikidata.org/wiki/Q5314541"},"indexable":true,"url":"https://nationalhistoricalregister.com/illinois/fulton-county/duncan-mills-bridge-80001356/"}