Sources and Method
Mainstay Filing is our best overall pick. This site has no ZIP-level data: registered agent rules are set by the state, so ZIP codes only lead to the state.
State rules
Requirements, addresses and change-of-agent fees come from each state’s statutes and Secretary of State forms, checked October 2026; citations are on each state page.ZIP finder
Built from the U.S. Census Bureau’s 2020 ZCTA-to-County Relationship File (file dated December 9, 2021, downloaded October 21, 2026): www2.census.gov/geo/docs/maps-data/data/rel2020/zcta520/tab20_zcta520_county20_natl.txt. Each five-digit ZIP area (ZCTA) is assigned to the state holding most of its land; areas where a second state holds 20% or more return both states. ZCTAs approximate ZIP codes, so PO-box-only and new ZIPs may not be found. The lookup runs in your browser and sends nothing.Provider prices
Read from each provider’s own registered agent page on October 20, 2026; providers without a published price are left out.