County in the Holy Roman Empire, in Swabia. The town of Calw is WSW of Stuttgart and SSE of Pforzheim and is today the administrative centre of the Landkreis of Calw in Baden-Württemberg.
The County was powerful and important in the 11th and 12th centuries – one member of its family, Godfrey, was appointed Count Palatine of the Rhine by Henry V in 1113 – but it fragmented as a result of partitions. Most of the lands of Calw eventually came to Württemberg, initially a much more insignificant County.
Baden, which is west of Calw, belonged to the Counts until the later 11th century when it passed by an heiress to the family which was to rule it until 1918. The County was partitioned in 1099, when the younger brother became Count of Löwenstein, which lay to the northeast beyond the River Enz (the Calw line there died out in the 13th century but Löwenstein survived as a County). The remainder of the County was partitioned in the later 12th century between the senior line at Calw and the junior line at Vaihingen (which was northeast of Calw and on the River Enz).
When the Calw line died out c.1263, the County was divided between the children of the two marriages of its heiress, one part to the Counts Palatine of Tübingen and the other to the Counts of Berg-Schelkingen, who sold it to Württemberg in 1308. The Tübingen share became part of Württemberg in 1345.
Württemberg also bought the lands of the Vaihingen line in the 1330s from the Count of Oettingen, who had recently bought them from the impoverished last survivors of the Counts of Calw.