I checked your message history, looks like you were looking for the marriage in Grimes and Walker Cos.Both of them weren't formed until 1846, both from Montgomery Co, TX.You might check that county, they have marriages back to 1838.Montgomery was formed from Washington Co, TX and they have marriages back to 1837.
"Republic of Texas: Poll Lists for 1846", compiled by Marion Day Mullins shows a Wm. R. Powell in Nacogdoches Co, TX.You might also try that county for a marriage.Nacogdoches has marriage records back to 1824.In the 1840 time frame it was still a pretty large county. Nacogdoches was the parent county to many other Texas counties that were formed later.It was considered the gateway into early TX. Happy Hunting (^_^)