Joan Kelly Horn (born October 18, 1936) is an American politician from Missouri.

She was elected to Congress in 1990, upsetting incumbent Republican Jack Buechner by 54 votes in a district that included most of St. Louis' western suburbs, such as Florissant, St. Charles, and Town and Country.

Earlier in 1990, the Democratic-controlled Missouri state legislature approved a new congressional district map that was intended to preserve heavy Democratic majorities in the two districts that included St. Louis itself — the 1st, represented by Democrat Bill Clay and the 3rd, represented by then-House Majority Leader Dick Gephardt.

However, the new map had been drawn well before the elections, and no one had anticipated Horn's upset win over Buechner.

In November 1992, Horn was narrowly defeated by Republican State House Minority Leader Jim Talent.