Smith Square is a square located in Westminster, part of the City of Westminster in London, which is notable for St. John's, Smith Square, the deconsecrated church in the middle of the square now used as a concert hall (especially for the BBC's lunchtime radio concerts). The square is notable in political history as the location of Conservative Central Office, the Conservative Party's headquarters since 1958 (shortly to be sold), and Transport House - now the headquarters of the Local Government Association but from 1928 to 1980 the headquarters of the Labour Party.

The square was named after the Smith family of landowners who live at number 1. Sir John Smith was Conservative MP for Cities of London and Westminster from 1965 to 1970.