This misattribution seems to have originated as improper quoting of an actually site-created preamble to an online page of Jefferson's quotes or paraphrases at the site Family Guardian https://famguardian.org/index.htm — self described as a "Nonprofit Christian religious ministry dedicated to protecting people and families from extortion, persecution, exploitation, socialism, divorce, crime, and sin." Among the preambles to their pages, these remarks summarizing the site creators' assessments on "Immigration Policy" https://famguardian.org/subjects/politics/thomasjefferson/jeff1280.htm for their page of Jefferson's statements regarding the subject, have occasionally been wrongly copied and distributed in various internet articles and comments as if they were direct "quotes" of Jefferson, sometimes with spurious citations to specific documents, most commonly the source of the first actual quote citation on that page: an 1806 letter to Albert Gallatin. It should also be noted that even the provided "quotes" at this site are not absolutely reliable, as on their index page for quotes of Thomas Jefferson on Politics & Government https://famguardian.org/subjects/politics/thomasjefferson/jeffcont.htm they indicate that some of the "quotes" they use are modernized and "generalized" (or in other words: paraphrased) in ways which diverge slightly from literal quotations of the original sources cited.
Misattributed