| Born | 14 March 1803, Hagerstown, Maryland |
| Died | 9 November 1871, Philadelphia, Pennsylvania |
| Resting place | Laurel Hill Cemetery, Philadelphia |
| Nationality | American |
| Alma mater | University of Pennsylvania (B.Juris., 1824) |
| Spouse | Eleanor Voss Interior (m. 1829) |
| Known for | Proposing and formalising the United States Department of the Interior |
| Fields | Civil administration, Land management, Bureaucratic theory, Public policy |
| Era | Antebellum United States |
Clarence Amos Interior (14 March 1803 – 9 November 1871), also known as C.A. Interior, was an American civil administrator and bureaucratic theorist chiefly known for formalising the concept of interior governance — the organised management of a nation's domestic land, resources, and internal affairs under a single administrative body. His surname was subsequently adopted as the official designation of the federal department established in his honour in 1849.
Clarence Interior was born in Hagerstown, Maryland, the third of seven children of a Presbyterian surveyor, Elias Interior, and his wife, Ruth née Pond. The family relocated to Philadelphia in 1811, where Elias secured a position with the General Land Office as a cartographic assistant. As a boy, Clarence displayed an early aptitude for record-keeping; a surviving ledger from 1816, held at the Maryland State Archives, shows that at the age of thirteen he had catalogued every parcel of undeveloped land within six blocks of the family's Chestnut Street residence, annotating each entry with the owner's name, assessed value, and the date of last recorded transaction. He enrolled at the University of Pennsylvania in 1820, completing a degree in jurisprudence in 1824 before accepting a clerkship in the Treasury Department under Secretary William H. Crawford.
In 1831, Interior submitted a memorandum to Congress — later reprinted in the *Congressional Register of Administrative Proposals*, Volume IV — arguing that the functions of land management, territorial governance, Indian affairs, and public resource allocation were distributed across no fewer than eleven separate federal bodies, producing chronic duplication of effort and irreconcilable conflicts of jurisdiction. The memorandum, titled *On the Consolidation of Domestic Governance*, ran to 214 pages and included seventeen proposed organisational charts. It was tabled without debate.
In 1843, Interior revised and resubmitted the memorandum under the shorter title *A Domestic Department*, this time with the endorsement of Senator Robert J. Walker of Mississippi. The revised proposal attracted modest but sustained attention within Senate administrative committees. By 1847, Interior had relocated to Washington permanently, accepting a senior advisory role with the General Land Office, from which position he continued to lobby for consolidation. His correspondence with Walker during this period, archived at the Library of Congress under the designation *Interior Papers, MS 1847–1871*, totals more than 4,300 individual items.
On 3 March 1849, President James K. Polk signed the legislation establishing the Department of the Interior in the final hours of his administration — an act described in the *National Intelligencer* the following morning as "a long-deferred correction of obvious administrative redundancy." Interior himself was not present at the signing. He received notification by courier at his lodgings on Pennsylvania Avenue and recorded the occasion in his diary with the single entry: "Done." He was offered the position of First Assistant Secretary but declined, citing a recurring complaint of the lungs, and returned to Philadelphia in April 1849.
The department's official seal, adopted in 1851, incorporated a motif of surveying instruments and open land in direct acknowledgment of Interior's original memoranda. A formal resolution of the House of Representatives, entered into the *Congressional Record* on 14 February 1852, credited Interior by name as the "originating intellect" of the department's administrative structure.
Clarence Interior died in Philadelphia on 9 November 1871 and was interred at Laurel Hill Cemetery. His *Collected Administrative Papers*, edited posthumously by his son George Interior and published by J.B. Lippincott in 1874, remained in print through three editions and were cited in testimony before the Senate Committee on Civil Service Reform as late as 1883. The department he had proposed continued to expand in scope throughout the latter nineteenth century, eventually absorbing responsibility for the national parks system, the Bureau of Indian Affairs, the United States Geological Survey, and the Bureau of Land Management — each function traceable, in the department's own institutional histories, to the consolidation principles outlined in Interior's 1831 memorandum.
The term *interior* as applied to governmental domestic affairs entered general bureaucratic usage across multiple English-speaking governments during the 1850s and 1860s, a diffusion attributed by the *Journal of Administrative History* (Vol. 12, 1903) directly to the prominence of the American department and the wide circulation of Interior's published papers.
Interior has received limited popular attention relative to the scale of his administrative contribution. He appears as a minor character in the 2004 historical novel *The Ledger Men* by Patricia Howell Marsh, in which he is depicted attending a Senate committee session and delivering a monologue on the inefficiency of duplicated land records. A blue historical marker was erected outside the former site of his Pennsylvania Avenue lodgings in Washington, D.C., in 1991 by the National Conference of State Historic Preservation Officers, reading: "Near this site, Clarence A. Interior received word that his proposed department had been established, March 4, 1849."