A spokesperson for the Post Office said the vacancy for a Truro branch had already been advertised.
It is going to have a "significant impact" on Horley, the local MP Chris Coghlan tells the BBC.
Residents warn that older and disabled people could struggle to access vital services.
The branch inside the TG Jones store on Bridge Street will be closing in early 2027.
The branch is shutting as it is inside a TG Jones store, which is also closing.
The Post Office says it hopes to open a replacement branch as soon as possible
The Post Office is looking for new premises when its current outlet closes in October.
Burpham Post Office is to shut its doors on Saturday, as 52 close across the country.
Rooprit Gill, falsely accused in the Horizon scandal, is back working at her former Post Office branch.
