Analysis
NAICS 928 is the 2022 subsector for national security and international affairs, part of 92 (Public Administration).
It has only one more detailed code, 9281, which covers exactly the same activities; the definition, index entries and statistics are on that page.
County Business Patterns excludes public administration, so there is no establishment count for it.
Official definition
The National Security and International Affairs subsector groups government establishments primarily engaged in national security and international affairs.
Source: US Census Bureau, NAICS 2022 Manual.