Thierry d'Alsace (c. 1099 - January 1168), sometimes known as Derry or Dirk, was count of Flanders from 1128 to 1168. He was the youngest son of Duke Thierry II of Lorraine and Gertrude of Flanders.

After the murder of Charles the Good, Thierry was one the claimants for the county. Due to the support of King Louis VI of France, William Clito became count instead. Thierry succeeded after William's death in 1128.

His first wife, Suanhilde, died in 1133, leaving an only daughter, Laurette. Laurette of Flanders married four times: (1) Ivan, Count of Alost; (2) Henry II of Limburg ; (3) Raoul I of Vermandois ; and (4) Henry I, Count of Luxembourg . Laurette finally retired to a nunnery, where she died in 1170.

Thierry secondly married Sibylle of Anjou, the former wife of William Clito. Their children were:

1. Philip of Flanders (died 1191)
2. Matthew of Alsace (died 1173), married Countess Marie of Boulogne
3. Margaret I of Flanders (died 1194), married Baldwin V, Count of Hainaut
4. Gertrude of Flanders (died 1186), married Humbert III of Savoy
5. Matilda, abbess of Fontevrault
6. Pierre, bishop of Cambrai (died 1176)

He was a noted Crusader, having undertaken four pilgrimages from 1139 to 1164. In 1139 he fought alongside his father-in-law Fulk V of Anjou at the invasion of Gilead. Afterwards he joined the Second Crusade, fighting at the Battle of Attalia in 1148; later that year he joined the assembly of King Baldwin III of Jerusalem at Acre. In 1164 he accompanied King Amalric I of Jerusalem to Antioch and Tripoli.

Sources

• Galbert of Bruges
• Runciman, Steven. A History of the Crusades, 1954.