I usually refer to this as "feet washing", though probably more people refer to it as "foot washing". In the early 1980s an older preacher told me it should be referred to as "feet washing" because you wash both feet, not just one. Since then I have tried to consistently refer to it in this manner. I hope to briefly explore feet washing and its history as it relates to Baptists, rather than discussing it from a theological perspective.
Which Baptists may or may not practice feet washing? Two groups that are most widely recognized as "feetwashers" are Primitive Baptists and Free Will Baptists, though the practice is not 100% among either of these. The majority of Primitive Baptists practice feet washing, but a few do not. Hassell mentions this in his History of the Church of God. Many Primitive Baptists refer to feet washing as an "example" rather than an ordinance. Feet washing is a majority practice among the Free Will Baptists, though, for example, it has been a little weak among Texas Free Will Baptists because of a strong link to the northern (Randall) version of Free Will Baptists. One Free Will Baptist church near here hasn't observed it in a number of years, though their statement of faith expresses a belief in it. Free Will Baptists seem to consistently refer to feet washing as an "ordinance".
Other lesser known or smaller groups of Baptists are fairly consistent "feetwashers", such as: Old Regular Baptists, United Baptists, Regular Baptists, General Baptists, Separate Baptists, and Interstate & Foreign Landmark Missionary Baptist Association. Central Baptists (Primitive Baptist descendants), Duck River and Kindred Associations, Two-Seed-in-the-Spirit Predestinarian Baptists, and Union Baptists (another Primitive Baptist descendant similar to the Regular Baptists) all practice feet washing.
Some other groups where one can find remnants of the practice are: missionary Baptists, Southern Baptists, and independent Baptists. It has a fairly strong minority following in these churches that are in the Appalachia region or its foothills (e.g., the Blue Ridge of north Georgia). A minority of country churches affiliated with the American Baptist Association and the Baptist Missionary Association used to practice feet washing, although I think the practice had been "rooted out" by mid-20th century. The last actual practice I have confirmed was a BMAA church in east Texas in 1954. A few local associations carried it in their minutes until the early 1960's. The split of the ABA in 1950, and the subsequent withdrawal of the majority of the "feetwashers" into the Interstate and Foreign Landmark Missionary Baptist Association probably finished what the seminaries had not done. An old issue of J. Frank Norris' paper (The Fundamentalist) indicates that in the early stages of the World Baptist Fellowship (then called the World Fundamental Baptist Missionary Fellowship), some of the churches among them practiced feet washing. I feel certain none do now.
Some sources that mention the subject. History of Middle Tennessee Baptists, by J. H. Grime [SBC], has a short chapter on the subject; The Lord's Table by W. J. Burgess [BMAA]; History of the Church of God by C. B. & Sylvester Hassell [Primitive Baptist]; History of the Franklin Association of United Baptists by W. P. Throgmorton [SBC]; The Baptists of Virginia by Garnett Ryland; The History of the English Baptists by Underwood; The Primitive Baptist newspaper, article by C. H. Cayce, Feb. 9. 1933; Foxfire 7. An interesting article on the subject of feet washing is found in Viewpoints: Georgia Baptist History, Volume 1. The article is titled "Feet Washing among Baptists of Georgia (A Study of)" by Charles O. Walker.
In general, the strength of feet washing in the United States was/is in the south, largely due to the influence of Shubal Stearns and the Separate Baptists. But also know that early on in the highly influential Philadelphia Baptist Association, they also approved it.