The Big Book of Cattle Brands
In order to ensure that your brand was the only brand of its kind, you had to record it with a governing authority of some kind. Usually, there was a statewide inspector and recorder of brands. While I didn't read the entire Marks and Brands book, most seemed to be from the Territory days, which could mean that, at the time, your county was the highest authority you had to report to. Or, it could be that, in interest of verifying your brand, you re-filed it with your local county for the benefit of the Sheriff. Regardless of how it originated, the book is a freakin' hoot to flip through. Here's the first couple pages:
For some scope: a hundred and twenty years ago, before the railroads, before statehood, some homesteader sat down under his kerosene lantern, drew out his brand, and took it to be filed. Glued to a page in a book and sealed by the Register of Deeds, his little sketch has lasted over a century, because it's the Recorder's job to make sure the information is stored indefinitely. Your own county has an office of its own, somewhere: the job's title has changed over the years, so check with your current County Recorder, Public Trustee, or Register of Deeds. They're the ones who need to use the information today, so they'll know where the records are. Most counties are open to the public, and the documents are largely items of Public Record, which means you shouldn't need permission to access them…although the genuine, centuries-old leatherbound books might not be directly available, in the interest of preservation. You might find some information here, as well as links to current brand books.