The Census Bureau has published a memo in the Federal Register that outlines residence criteria and residence situations that determine who should be counted and where they should be counted. Federal employees working overseas are specifically mentioned in this memo.
For the 2020 Census, the Census Bureau outlines these specific situations involving military and federal employees overseas and how it will count them:
Overseas military and civilian employees of the U.S. government — The 2020 Census will count military and civilian employees of the U.S. government who are temporarily deployed overseas on Census Day at their usual home address in the United States, as part of the resident population, instead of their home state of record. Military and civilian employees of the U.S. government who are stationed or assigned overseas on Census Day, as well as their dependents living with them, will continue to be counted in their home state of record for apportionment purposes only.
Overseas federal employees who are not U.S. citizens — The 2020 Census will count any non- U.S. citizens who are military or civilian employees of the U.S. government who are deployed, stationed, or assigned overseas on Census Day in the same way as U.S. citizens who are included in the federally affiliated overseas count.
The memo is part of the agency’s 2020 Census Memorandum Series which documents significant decisions, actions, and accomplishments of the 2020 Census Program for the purpose of informing stakeholders, coordinating interdivisional efforts, and documenting important historical changes.