Saint-Justin (French pronunciation: [sɛ̃ ʒystɛ̃]; Occitan: Sent Justin) is a commune in the Landes department in Nouvelle-Aquitaine in southwestern France.

In 1280, Constance Viscountess de Marsan signed an “acte de paréage” (a shared sovereignty agreement) with the Order of chivalry of the Hospitallers of St. John of Jerusalem, with which they founded the new Bastide of Saint-Justin. This agreement was signed without the authorization of Edward I, King of England, then Duke of Aquitaine.

The fortified town of Saint-Justin has the typical rectangular central square covered with arches and surrounded by half-timbered and stone houses with mullioned windows. Under the arcades, there are many shops, providing a walk for pedestrians and shelter from sun and rain. The town has three octagonal towers and a walkway along the ramparts and the tower wall.

Historical population

Year	Pop.	±% p.a.
1968	1,082	—
1975	973	−1.51%
1982	914	−0.89%
1990	917	+0.04%
1999	888	−0.36%
2009	922	+0.38%
2014	985	+1.33%
2020	1,008	+0.39%
Source: INSEE

• Château de Fondat
• Communes of the Landes department