In 1870, the U.S. marshals appointed assistants to conduct the census, so the hiring of assistants was at their discretion. In 1880 and 1890, the temporary census office hired enumerators. The records in NARA’s possession do not include comprehensive lists of either the assistant U.S. marshals who conducted the census (1790-1870) or of census enumerators (1890-1950).
It’s possible that the reports published following the taking of each decennial census include references to racial composition of the enumerators - these for 1790-2020 are available on the Census Bureau’s website at https://www.census.gov/programs-surveys/decennial-census/decade.html.
Newspaper articles may also be a good source of information. Historical newspaper articles are digitally available on websites such as the Library of Congress’s Chronicling America website at https://chroniclingamerica.loc.gov (free), and on commercial sites such as Newspapers.com (fee) and GenealogyBank.com (fee). For example, the article, “Twelve Hundred Colored Enumerators Appointed,” The Broadaxe (Chicago, Illinois), April 16, 1910, page 1, indicates that the 1,200 “colored” [sic] enumerators appointed for the 1910 census was the largest number ever, and that they would “take the census of their own people in districts where they constitute two-fifths or more of the total population.” See https://chroniclingamerica.loc.gov/lccn/sn84024055/1910-04-16/ed-1/seq-1/#date1=1910&index=2&rows=20&words=Colored+enumerated+enumerators&searchType=basic&sequence=0&state=Illinois&date2=1910&proxtext=%22colored+enumerator%22&y=10&x=14&dateFilterType=yearRange&page=1
A search for “colored enumerator” with the year 1880 found one paragraph repeated in several newspapers about a “colored enumerator” in Columbus, Ohio, who could record 200 people a day with a pencil held in his mouth - which he had to do, having lost both arms to amputation at the shoulder. https://chroniclingamerica.loc.gov/lccn/sn86053659/1880-09-10/ed-1/seq-1/#date1=1880&index=0&rows=20&words=colored+enumerator&searchType=basic&sequence=0&state=&date2=1880&proxtext=%22colored+enumerator%22&y=11&x=14&dateFilterType=yearRange&page=1. Certainly, further research (with these or other search terms) may provide additional information.
Also, Census Bureau Historian Christopher Martin did a presentation on “Diversity at the Census Bureau” - link to transcript and video here: https://www.census.gov/data/academy/webinars/2021/diversity-at-the-census.html that discusses the first African American marshal and early enumerators of color.
Thank you so much; very helpful. m.