Duane's take
Here's how the official marker tells it, and I'll do my best to do it justice. Way out in the piney woods of East Texas, there's a county with a name that starts with a story older than the state itself. Eighteenth century Spanish explorers were pushing through this country, and they came upon a stream so thick with water hyacinths you could practically walk across it on the blooms.
So they did what explorers do. They gave it a name. They called it after Saint Hyacinth, and that name stuck to the stream, and the stream's name stuck to the county, and here we are.
Anglo-Americans began settling the area after 1820, planting roots in that hyacinth country, building something out of the wilderness one year at a time. When the time came to draw lines on a map and make it official, the new county was carved from portions of Polk, Montgomery, Liberty, and Walker counties. Four neighbors giving up a little ground each to make something new.
San Jacinto County was created on January 5, 1869. Now, you'd think that would be the end of the paperwork. But Texas being Texas, the county had to be recreated on August 13, 1870, and then organized on December 1 of that same year.
Three separate official moments before the thing really took hold. When the dust finally settled, the county had its seat, and they called it Cold Springs in 1870. Later, the name smoothed itself out to Coldspring, one word, neat and clean.
A Spanish saint, a flower-choked stream, four borrowed counties, and a town that couldn't quite decide how to spell its own name. That's San Jacinto County, and it's been telling that story ever since.
What the marker says
Eighteenth century Spanish explorers gave to the hyacinth-choked stream the name of Saint Hyacinth. Anglo-Americans settled here after 1820. Formed from portions of Polk, Montgomery,, Liberty and Walker counties. Created January 5, 1869; recreated August 13, 1870; organized December 1, 1870. County seat, Cold Springs, 1870; later, Coldspring.