Eugenics is a modern invention, based in the science of evolution (and the pseudo-science of evolution, such as Lamarckian ideas of inheritability of acquired traits!).

What may interest you is that eugenics did have quite a following in the US in the Progressive Era - around the same time that other experts are professionalizing and asserting their status in American culture on the basis of their scientific and technical knowledge. For example, at the Panama-Pacific International Exposition of 1915 (one of the World's Fairs in the pattern of the Colombia Exposition of 1893 in Chicago that is better known), the Race Betterment Foundation was a strong presence. They made a number of compelling presentations and used the Exposition as a platform to network among all sorts of doctors of colonial/imperial and, because of the Exposition location, largely tropical medical doctors to talk about how to uplift lower races and protect the advance of the white race. Ideas of quarantine for the ill and of prophylactics for sex -- for the 'lesser races' were advocated strongly and loudly - and without much of any controversy! This was a 'scientific' and elite philosophy, held only by those metropolitan enough to know about the world and with access to education.

However, more dilute versions of eugenics occurred in the American lay population before the Nazis came to power, especially along the Texas-Mexican border in the 1920s. At this time, there was a general up-surge of Nativist (meaning anti-immigrant) sentiment in the United States--the ultimate proof of which is the Immigration Restriction Act of 1921, first setting quotas limits on the number of foreign nationals that could enter the US, and the 1924 Johnson-Reed, or Immigration Act, which lowered those limits to 2% of the number of that country's nationals currently already living in the US. In other words, if you had 100 Narnian nationals already registered as living in the US, only 2 more could enter the country per year.

While it is important not to conflate this nativist sentiment with actual eugenics, it goes to show that some of the basic tenets of eugenics -- such as valuing educated, native-born Anglo-Saxons over all others and seeking to preserve homogeneity of the population -- were hardly repugnant to Americans essentially until the aftermath of World War Two when America had to grapple with the atrocities of Hitler's genocidal regime. As historian Alexandra Stern notes,

Hereditarianism, however, did not perish after World War II; it was repackaged. Exhibiting more flexibility than their predecessors, postwar eugenicists partly accepted the role of extrinsic factors and incorporated tenets from demography, sex research, psychoanalysis, and anthropolgy into their repertoires. [...] After World War II as the US became a global superpower, a core group of eugenicists merged their interest in salvaging and retooling eugenics with the export of Western-led modernization to the Third World.

Perfect examples of this are the postwar policies of Planned Parenthood, the Population Council, and neo-Malthusians--including some environmental Malthusians.

Hope this helps!

SOURCE: [mostly] Alexandra Stern, Eugenic Nation: Faults and Frontiers of Better Breeding in Modern America (Berkeley: University of California Press, 2005).

EDIT: Another great book around a closely related subject that reiterates some of this information and goes into much more detail on earlier eugenic-style ideologies scared of 'racial decline' due to mixing with African Americans is Peggy Pascoe, What Comes Naturally: Miscegenation Law and the Making of Race in America (Oxford, England; New York, NY: Oxford University Press, 2009). If you are looking for examples of American colonist eugenics in practice, see Laura Briggs, Reproducing Empire: Race, Sex, Science, and U.S. Imperialism in Puerto Rico (Berkeley: University of California Press, 2002) - she discusses the forced sterilizations of Puerto Rican women carried out under US medical auspices and the ideologies that guided such actions, among a number of other depressing topics.