The Hagrites appear very few times in the Bible. In 1 Chronicles 5:10, 19-20 a conflict is described between the tribe of Reuben and the Hagrites and their allies. This indicates that the Hagrites dwelled east of the Jordan. It is also recorded that David had a Hagrite in his service, who took care of the sheep (1 Chronicles 27:31). Finally, in Psalm 83:7 the Hagrites are named as one of the nations that wanted to exterminate Israel.
The Hagrites are generally seen as descendants of Hagar. Because in both 1 Chronicles 5 and 1 Chronicles 27, a clear distinction is made between the Ishmaelites and Hagrites, they must be two different nations. The most obvious conclusion is that Hagar re-married and had children, who later were called Hagrites and settled near their relatives, the Ishmaelites.
Note: One of King David’s heroes is Mibhar son of Hagri (1 Chronicles 11:38). Because in Hebrew this name has the same consonants as Hagrite, he possibly belonged to the tribe of the Hagrites, but this cannot be determined with certainty.