DeGroot's early coaching career included Santa Barbara State College, which is now one of the University of California campuses, and Menlo Junior College, the college level portion of Menlo School which became Menlo College in 1927 and now is independent, although they continue to share the same campus.
From 1932 through 1939, DeGroot was the head football coach at San Jose State University, where he put together a 59–19–8 record for the Spartans. His best season there came in 1939, when his team went undefeated and had outscored opponents 324 to 29. As of 2006 on a list published on Mercury News of the seven biggest turnarounds for a single season in the history of the Spartans, only DeGroot is listed twice, for 1932 and 1937. The statistics for these are: the record for the 1932 season is 7–0–2 with a previous season of 1–7 and a margin of six and, the record for the 1937 season is 11–2–1 with a previous season of 5–4 and another margin of six.
His next team leadership was at the University of Rochester, where he was football coach from 1940 through 1943. DeGroot's record there was 24–6.
DeGroot received his doctorate degree in education and was recognized as one of the foremost oologists and ornithologists in the United States. His work in oology continues to be discussed in scientific publications.
Notable members of his immediate family include his son, Dudley E. DeGroot, who obtained his doctorate degree in anthropology  and one of his daughters, Sally, who became a large animal veterinarian.
^An Historic Resources Survey of the Coastal Zone of Sarasota County, Florida, prepared for the Sarasota County Board of County Commissioners, Sarasota County Department of Natural Resources, and the Sarasota County Department of Historical Resources by the University of South Florida Department of Anthropology, Tampa, Florida for the Florida Department of Environmental Regulation per CM.235 Agreement for Cultural Resources Management; March 1990, pp. 5, 213 "...A great deal of information was generously shared by colleagues and concerned Sarasota County residents. We wish to acknowledge the special contributions of the following: ... Kafi Benz, Dudley deGroot ..."