{"nrhp_refnum":"75000675","name":"Thompson Mill Covered Bridge","other_names":[],"category":"structure","location":{"address":"0.5 mi. NE of Cowden over Kaskaskia River","address_restricted":false,"city":"Cowden","county":"Shelby County","state":"IL","lat":39.25837138300005,"lon":-88.81812181599997,"geom_source":"nps_gis"},"listed_date":"1975-03-13","is_nhl":false,"nhl_designated_date":null,"areas_of_significance":["Engineering","Transportation"],"significance_levels":["state","local"],"summary":{"what_it_is":"A wooden covered bridge with a Howe truss span over the Kaskaskia River about 0.5 mile north of Cowden, Shelby County, Illinois. The form gives its construction date as 1868 in the text and about 1857 in other entries.","why_significant":"The nomination argues it is significant for its type of structure, its age and its continuous use. It is one of only eight remaining 19th-century covered bridges in Illinois and the narrowest of them. It also reflects 19th-century horse-and-buggy road construction and the nearby Thompson Mill.","narrative":"Spanning the Kaskaskia River just north of Cowden in Shelby County, Illinois, this wooden covered bridge carries traffic on a township road. Its main span uses a Howe truss, with vertical iron tension rods and crossed wooden diagonals, and measures 103 feet 4 inches between piers, with steel I-beam approach spans at each end. The piers are tubular iron shells filled with shale. The form says the bridge was fabricated in Michigan, shipped to Shelbyville and hauled to the site by horse-drawn wagon, and it is named for the nearby Thompson Mill, a corn and saw mill that operated until 1914. The road once linked Springfield, Taylorville and Effingham and served local farms. At just 10 feet 7 inches wide, it is the narrowest of the eight 19th-century covered bridges left in Illinois. Its original timbers remain, and the roof and siding have been repaired several times, most recently in the 1960s. A state historical marker was dedicated in 1972.","period_of_significance":"19th Century (specific date given as about 1857)","architect_builder":null,"architectural_style":"Howe truss covered bridge; frame construction with vertical siding","criteria":[],"status_note":"Excellent condition, unaltered, on its original site; still used by vehicular traffic on a township road. Roof and siding restored, with railings and approach beams altered in 1973 to restore the original appearance.","vacant_flag":false,"machine_generated":true,"model":"claude-sonnet-5-5","prompt_version":"v1.0-2026-10-29","generated_at":"2026-10-29 02:55:35.049777-05","source_pdf":"https://s3.amazonaws.com/NARAprodstorage/opastorage/live/19/8941/28894119/content/electronic-records/rg-079/NPS_IL/75000675.pdf"},"photo":{"url_800":"https://nationalhistoricalregister.com/media/75000675/c04547a4aa-800.webp","url_1600":"https://nationalhistoricalregister.com/media/75000675/c04547a4aa-1600.webp","licence":"Public domain","author":"Nyttend","credit_html":"<a href=\"https://commons.wikimedia.org/wiki/File:Thompson_Mill_Covered_Bridge_from_southwest.jpg\" rel=\"noopener\">Nyttend</a>, Public domain, via Wikimedia Commons","source_page":"https://commons.wikimedia.org/wiki/File:Thompson_Mill_Covered_Bridge_from_southwest.jpg"},"district":null,"sources":{"nps_snapshot_date":"2026-05-22","nara_catalog":"https://catalog.archives.gov/id/28894119","wikipedia":"https://en.wikipedia.org/wiki/Thompson_Mill_Covered_Bridge","wikidata":"https://www.wikidata.org/wiki/Q16901614"},"indexable":true,"url":"https://nationalhistoricalregister.com/illinois/shelby-county/thompson-mill-covered-bridge-75000675/"}