{"nrhp_refnum":"71000294","name":"Duncan, Joseph, House","other_names":["Governor Duncan Mansion","Elm Grove","Rev. James Caldwell Chapte"],"category":"building","location":{"address":"4 Duncan Pl.","address_restricted":false,"city":"Jacksonville","county":"Morgan County","state":"IL","lat":39.733517131500065,"lon":-90.24915525549383,"geom_source":"nps_gis"},"listed_date":"1971-11-05","is_nhl":false,"nhl_designated_date":null,"areas_of_significance":["Education","Politics/Government","Architecture"],"significance_levels":["national","state"],"summary":{"what_it_is":"A three-story oak frame mansion with black walnut weatherboarding at No. 4 Duncan Place, Jacksonville, Morgan County, Illinois, begun in 1833 as the home of Governor Joseph Duncan.","why_significant":"The nomination argues the house is significant for its association with Joseph Duncan, a state senator, congressman and Illinois governor who championed free public schools and the Illinois and Michigan Canal. It also presents the original house as an example of early Georgian Colonial architecture adapted to Illinois, and notes it served as the governor's residence while Vandalia was the capital.","narrative":"Joseph Duncan's mansion in Jacksonville, Illinois, known as Elm Grove, was begun in 1833 and became the permanent home of the future governor. The three-story oak frame house is covered in black walnut weatherboarding and has sixteen rooms. Originally it had two side wings and a symmetrical facade with a steep roof and a semicircular fanlight, features of early Georgian Colonial design that the nomination links to Duncan's father's house in Kentucky. The wings were removed, and porches, a porte cochere, maids' quarters and a rear kitchen were added in 1882 and 1900. Duncan served as state senator, drafting a 1825 public school law, then as the sole Illinois congressman from 1827 to 1833, and as governor from 1834. He pressed for the Illinois and Michigan Canal. Because Vandalia had no official governor's residence, this mansion served that purpose. Later it housed an institution for children, and a Daughters of the American Revolution chapter now uses it as a museum.","period_of_significance":"19th Century","architect_builder":null,"architectural_style":"Colonial architecture of the early Georgian type","criteria":[],"status_note":"Described as altered and in deteriorated condition at nomination; occupied and used as a museum by a Daughters of the American Revolution chapter. Later grant paperwork funds restoration of interior walls, plumbing, furnace and shutters.","vacant_flag":false,"machine_generated":true,"model":"claude-sonnet-5-5","prompt_version":"v1.0-2026-10-29","generated_at":"2026-10-29 02:55:35.831705-05","source_pdf":"https://s3.amazonaws.com/NARAprodstorage/opastorage/live/69/8937/28893769/content/electronic-records/rg-079/NPS_IL/71000294.pdf"},"photo":{"url_800":"https://nationalhistoricalregister.com/media/71000294/6aa361da73-800.webp","url_1600":"https://nationalhistoricalregister.com/media/71000294/6aa361da73-1600.webp","licence":"Public domain","author":"Nyttend","credit_html":"<a href=\"https://commons.wikimedia.org/wiki/File:Joseph_Duncan_House.jpg\" rel=\"noopener\">Nyttend</a>, Public domain, via Wikimedia Commons","source_page":"https://commons.wikimedia.org/wiki/File:Joseph_Duncan_House.jpg"},"district":{"nrhp_refnum":"14000509","name":"Jacksonville Historic District (Additional Documentation, Boundary Increase)","url":"https://nationalhistoricalregister.com/districts/illinois/jacksonville-historic-district-additional-documentation-boundary-increase-14000509/"},"sources":{"nps_snapshot_date":"2026-05-22","nara_catalog":"https://catalog.archives.gov/id/28893769","wikipedia":"https://en.wikipedia.org/wiki/Joseph_Duncan_House","wikidata":"https://www.wikidata.org/wiki/Q19872795"},"indexable":true,"url":"https://nationalhistoricalregister.com/illinois/morgan-county/duncan-joseph-house-71000294/"}