diff --git a/changelog/18598.txt b/changelog/18598.txt
new file mode 100644
index 000000000000..62d13d0e705f
--- /dev/null
+++ b/changelog/18598.txt
@@ -0,0 +1,3 @@
+```release-note:bug
+core/activity: include mount counts when de-duplicating current and historical month data
+```
diff --git a/vault/activity_log.go b/vault/activity_log.go
index 24df0213e2fc..3c4bc613da26 100644
--- a/vault/activity_log.go
+++ b/vault/activity_log.go
@@ -1598,15 +1598,37 @@ func (a *ActivityLog) handleQuery(ctx context.Context, startTime, endTime time.T
 		}
 
 		// Rather than blindly appending, which will create duplicates, check our existing counts against the current
-		// month counts, and append or update as necessary.
+		// month counts, and append or update as necessary. We also want to account for mounts and their counts.
 		for _, nrc := range byNamespaceResponseCurrent {
 			if ndx, ok := nsrMap[nrc.NamespaceID]; ok {
 				existingRecord := byNamespaceResponse[ndx]
+
+				// Create a map of the existing mounts, so we don't duplicate them
+				mountMap := make(map[string]*ResponseCounts)
+				for _, erm := range existingRecord.Mounts {
+					mountMap[erm.MountPath] = erm.Counts
+				}
+
 				existingRecord.Counts.EntityClients += nrc.Counts.EntityClients
 				existingRecord.Counts.Clients += nrc.Counts.Clients
 				existingRecord.Counts.DistinctEntities += nrc.Counts.DistinctEntities
 				existingRecord.Counts.NonEntityClients += nrc.Counts.NonEntityClients
 				existingRecord.Counts.NonEntityTokens += nrc.Counts.NonEntityTokens
+
+				// Check the current month mounts against the existing mounts and if there are matches, update counts
+				// accordingly. If there is no match, append the new mount to the existing mounts, so it will be counted
+				// later.
+				for _, nrcMount := range nrc.Mounts {
+					if existingRecordMountCounts, ook := mountMap[nrcMount.MountPath]; ook {
+						existingRecordMountCounts.EntityClients += nrcMount.Counts.EntityClients
+						existingRecordMountCounts.Clients += nrcMount.Counts.Clients
+						existingRecordMountCounts.DistinctEntities += nrcMount.Counts.DistinctEntities
+						existingRecordMountCounts.NonEntityClients += nrcMount.Counts.NonEntityClients
+						existingRecordMountCounts.NonEntityTokens += nrcMount.Counts.NonEntityTokens
+					} else {
+						existingRecord.Mounts = append(existingRecord.Mounts, nrcMount)
+					}
+				}
 			} else {
 				byNamespaceResponse = append(byNamespaceResponse, nrc)
 			}