Stephen Jay Gould wrote an entire book about this kinda stuff, called The Mismeasure of Man which I highly recommend. The short answer is, lots.

In my own realm of study, anthropology, probably the most... robust attempts were made by Carleton Coon and Aleš Hrdlička. Coon published an encyclopedic book on the origin of races, postulating that humans evolved in Africa (Negroid) and then further evolved into Caucasoid, Asiatic, etc. after leaving Africa. Which is at least close to the truth, although we didn't "split into races" so much as "adjust a few features for local conditions." And the notion that we kept on evolving post-Negroid de facto suggests that African people are less evolved than everyone else.

As for Hrdlička, you might as well call him the father of eugenics, although he technically wasn't. He espoused similar ideas about human evolution producing the different "races" but pushed it a bit further, comparing the brain weights of different non-white cadavers and attempting to catalog racial groupings by skull shape and so on. Again, not terribly far from the truth--e.g., Native Americans very often have shovel-shaped incisors--but (a) it's entirely statistical, often with greater variability within so-called racial groups than between them; and (b) it still doesn't really tell you anything about them, but that didn't stop Hrdlička and colleagues from assuming a gradient in terms of superiority. Hence his merging of cladistical categorizing with genetic science to arrive at the conclusion that you can breed out the bad bits.

There are others, of course, but those two are useful to talk about because they were such highly regarded scientists and just like this close to realizing race can't be objectively quantified and measured. Because it's a social convention.

Edit: grammar. As always.

You may be interested in James Whitman's "Hitler's American Model: The United States and the Making of Nazi Race Law."

When the Nazis were seeking examples on how to legally codify "race" they looked across the Atlantic to the country that had the worlds most sprawling apparatus of racial legislation and judicial precedent.

From blood quantum laws for indigenous people, to extensive legislation and litigation restricting asian people especially in Western states, to racially-based immigration laws passed in the 1920s, to the varied Jim Crow regimes of the Southern States, the drafters of the Nuremburg Laws had ample material to examine, compare, contrast, and adapt for their own purposes.

As just one example of how this ocurred, Hans Krieger was a German jurist who spent time at the University of Arkansas in 1933-34, in part to study American racial laws (his particular focus was on Indigenous people). Upon his return he was connected with officials in the Justice Ministry, and a detailed memorandum he produced on the Jim Crow legal regime was influential in key discussions that drafted the infamous Nuremburg laws. Whitman argues that it had particular influence on the anti-miscegenation laws implemented in 1935.

One thing Krieger and others noticed was that there was no uniform means of defining race in the United States. While many individual states had legally codified regimes, these could vary in how ones race was determined as well as the implications thereof. Some states practiced a "one drop rule" wherein anyone with any ancestry defined as "non-white" was considered 'colored.' In much of the South this often took the form of essentially a black/white dichotomy, wherein people of other background found it messy to navigate whrere they fit in. (For one example of this complexity, I would recommend Moon Ho Jung's "Coolies and Cane: Race, Labor, and Sugar in the Age of Emancipation" which focuses on Chinese people working on post-civil war plantations.) Other states defined based on some fraction of non-european heritage. A controversial legacy of this can be seen in the blood quantum laws many Tribal bodies have adopted over the years, often under pressure from the federal government. One can only be an enrolled member of most tribes based on a proportion of "blood" as determined by descent from old tribal rolls.

Im afraid I dont have the sources at hand to get into the nuance of how US racial policy played out everywhere, but I hope you found this late comment useful.