Thompson's Island Homeplace
San Marcos, Hays County, Texas
Marker Inscription
Dr. William Alexander Thompson (1803-1879) made an agreement with neighbors in 1850 to use the San Marcos River for irrigation and as a source of energy. He and his sons William A. and James used slave labor to build a gristmill, sawmill and cotton gin. The land masses formed by digging a ditch for the waterwheel and a sluiceway from the river were called "Thompson Islands." The Thompsons directed the business until 1911 when John Matthew Cape (1861-1933) bought the mill. The use of electricity in 1942 ended the mill's need for water power.
Erected by Texas Historical Commission
The Story
In 1850 Dr. William Alexander Thompson struck an agreement with his neighbors to harness the San Marcos River, and he and his sons used enslaved laborers to build a gristmill, sawmill, and cotton gin. The channels dug for the waterwheel created the parcels known as "Thompson Islands." The family ran the mills until 1911, and the arrival of electricity in 1942 finally ended the site's dependence on water power.
Why it matters
The mill complex shows how antebellum Texas industry was built on the labor of enslaved people and the power of its rivers.
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Related people
- · William Alexander Thompson
- · John Matthew Cape
Themes & tags
Nearby & related markers
Thompson's Islands
San Marcos, TX
William A. Thompson moved his family and the people he enslaved from Louisiana to Texas in 1850, establishing plantations in Caldwell and Hays counties. Enslaved laborers built a mill on the San Marcos River whose construction reshaped the channel into three small islands still called Thompson's Islands. The mill powered local lumbering and a cotton gin, anchoring the area's antebellum economy for generations.
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