Adelphi is an unincorporated community in Polk County, in the U.S. state of Iowa.

Adelphi was platted on April 6, 1857, in Camp Township.

No railroad line was built to the community, inhibiting its growth, and leaving it as what one 1876 Polk County historian called a village.

[2] Adelphi's post office was established in 1856.

The Altoona Herald observed, "Adelphi's loss is Runnells' gain".