Commissions are usually composed of two county supervisors selected by the Board of Supervisors; two city council representatives selected by a majority of the mayors in the county; and one public member selected by the other four members. Commission members serve four-year terms. There is an alternate for each category - city, county, and public.

Composition of Local Agency Formation Commissions may vary in other counties. Several LAFCOs have independent special district representation on the Commission, thereby expanding to seven members. Also some LAFCOs, including: Los Angeles, Santa Clara, and San Diego, have, through special legislation, reserved a seat on the Commission for a representative from the county's major city.