{"nrhp_refnum":"04000181","name":"Lock and Dam No. 21 Historic District","other_names":[],"category":"district","location":{"address":"0.5 mi. W of IL 57","address_restricted":false,"city":"Quincy","county":"Adams County","state":"IL","lat":39.906212442000054,"lon":-91.43140756638127,"geom_source":"nps_gis"},"listed_date":"2004-03-10","is_nhl":false,"nhl_designated_date":null,"areas_of_significance":["Transportation","Maritime History","Social History","Commerce","Conservation","Economics","Politics/Government","Military"],"significance_levels":["national"],"summary":{"what_it_is":"A 107.46-acre federal navigation district on the Upper Mississippi River just downstream from Quincy, Illinois, made up of a lift lock, a nonnavigable dam, a control station, an esplanade and related features, built mainly between 1933 and 1938.","why_significant":"The district is part of the Upper Mississippi River 9-Foot Navigation Project and is listed under Criterion A. Its roller gates helped shape the American-style submersible roller gate, and the project was moved up in the construction order to provide relief work in Quincy, which had acute unemployment. The district keeps its original configuration and setting.","narrative":"Lock and Dam No. 21 crosses the Upper Mississippi River just downstream from Quincy, Illinois. The 107.46-acre district includes a lift lock with a 10.5-foot lift, an incomplete auxiliary lock, a dam with ten Tainter gates and three submersible roller gates, a central control station, and a landscaped esplanade about 2,000 feet long. Most of it was built between 1933 and 1938 as a federal relief work project, and Quincy was favored in the construction order because of its severe unemployment. Joseph Meltzer Construction built the lock, and McCarthy Improvement Company built the dam, which opened to navigation on July 23, 1938. The roller gates, designed in 1936 to submerge only 4.67 feet, served as the model for later gates on the river system. Guard wall and guide wall additions in 1942 and 1951 addressed outdraft problems at the lock entrance. A major rehabilitation between 1985 and 1994 replaced much of the machinery and added new buildings, yet the district keeps its original layout and open river setting.","period_of_significance":null,"architect_builder":"Joseph Meltzer Construction (lock, control station, esplanade); McCarthy Improvement Company of Davenport, Iowa (dam); designed by Rock Island District engineers, U.S. Army Corps of Engineers","architectural_style":"OTHER: lock and dam; NO STYLE: control station; OTHER: machinery","criteria":["A"],"status_note":"In continuous use as part of the Upper Mississippi River 9-Foot Channel Project since July 23, 1938; the form rates condition as excellent after a 1985-1994 major rehabilitation.","vacant_flag":false,"machine_generated":true,"model":"claude-sonnet-5-5","prompt_version":"v1.0-2026-10-29","generated_at":"2026-10-29 02:55:37.566839-05","source_pdf":"https://s3.amazonaws.com/NARAprodstorage/opastorage/live/7/8907/28890707/content/electronic-records/rg-079/NPS_IL/04000181.pdf"},"photo":{"url_800":"https://nationalhistoricalregister.com/media/04000181/e3c53c3fe4-800.webp","url_1600":"https://nationalhistoricalregister.com/media/04000181/e3c53c3fe4-1600.webp","licence":"Public domain","author":"Peter A. Rathbun","credit_html":"<a href=\"https://commons.wikimedia.org/wiki/File:Mississippi_River_Lock_and_Dam_number_21_HAER.jpg\" rel=\"noopener\">Peter A. Rathbun</a>, Public domain, via Wikimedia Commons","source_page":"https://commons.wikimedia.org/wiki/File:Mississippi_River_Lock_and_Dam_number_21_HAER.jpg"},"district":null,"sources":{"nps_snapshot_date":"2026-05-22","nara_catalog":"https://catalog.archives.gov/id/28890707","wikipedia":"https://en.wikipedia.org/wiki/Lock_and_Dam_No._21","wikidata":"https://www.wikidata.org/wiki/Q1867486"},"indexable":true,"url":"https://nationalhistoricalregister.com/illinois/adams-county/lock-and-dam-no-21-historic-district-04000181/"}