The County of Saarwerden (German: Grafschaft Saarwerden; French: Comté de Sarrewerden) was a county located in Lorraine, within the Holy Roman Empire. As a second-level fief, it belonged to its local ruler and not to the emperor. Its capital was in Bockenheim [de; fr] (situated on the right side of the Saar) and later in New Saarwerden or Ville Neuve de Sarrewerden (on the left side of the Saar), both in the present city of Sarre-Union. Today, the area of the county belongs to Bas-Rhin, Alsace.

In 1047, Emperor Heinrich III of the Holy Roman Empire established the Duchy of Lorraine from the former Duchy of Upper Lorraine. During the troubles that agitated the duchy, some lords rebelled and became more or less, independent of the Duke. Saarwerden branched from the Bishopric of Metz, when lord Friedrich, son of Godfrey I of Blieskastel separated and formed the County of Saarwerden. Thus the county was created under the House of Saarwerden in 1111. Friedrich built a castle in Sarrwerden upon the ruins of an ancient Roman bath. He and his wife Gertrude also founded the Abbey Wörschweiler in 1130.

The most famous representative of this family was Friedrich III. He was Archbishop of Cologne from 1370 to 1414. On the death of his childless brother Heinrich II, the last Count of Saarwerden, in 1397, Friedrich temporarily directed the county before ceding the government to his stepbrother, Friedrich III, Count of Moers.

Now the county was in personal union under Friedrich as the County of Moers-Saarwerden. In 1417, the County of Saarwerden branched off once more as the inheritance of his son, Johann. The House of Moers-Saarwerden died to the House of Nassau and County of Saarbrücken in 1527; through jure uxoris, Johann Ludwig of Nassau-Saarbrücken inherited the lands of his wife, Countess Katharina I.

The county was passed into the House of Nassau. Count Johann Ludwig attempted to usurp the authority of the Bishopric of Metz in the county by dissolving the Benedictine Abbey in 1554. After the Abbey was demolished in 1557, The Bishopric of Metz was annexed into France, and the land passed to Lorraine. Old property disputes with Lorraine were a subject of contention during this time.

Count Adolf introduced the Reformation into Saarwerden in 1556. He allowed Protestant refugees fleeing religious persecution in the Kingdom of France and the Duchy of Lorraine. He approved the settlement of what became known as 'Seven Gallic Villages': Altwiller, Burbach, Diedendorf, Eywiller, Gœrlingen, Kirrberg, and Rauwiller. Thus, the county was populated with Calvinists who spoke French, while the rest of the county were Lutheran Germans. The County of Saarwerden become an experimental model of peace between Lutherans and Calvinists. Since Adolf died childless, the County fell back to his Catholic brother, Johann V. Johann did not persecute the Protestants, however.

There was much contention between the Catholic Lorraine and the newly Protestant Saarwerden. When Protestant Philip II inherited the lands in 1574, Duke Charles III of Lorraine demanded Saarwerden back as a completed fief (meaning Philip was without any heirs). The dispute went on for many years and threatened several times to escalate to military level. The Elector Palatine, Frederick III also claimed parts of the inheritance. Here too, the House of Nassau managed to prevail on the essential points. Several large treaties were closed, in which the exact rights and boundaries of the Nassau and Palatinate territories were defined.

In 1575 Philip introduced the Reformation in his territories. Catholic priests were converted to the new faith or removed from office; church property was confiscated; schools were established and patronage was acquired. His implementation of the Reformation intensified his disputes with the Duchy of Lorraine, which was still Catholic. The County grew and prospered under Philip's son Ludwig IV. The Thirty Years' War also started in this time.