Marriage license
Getting a Marriage License at the Tom Green County Courthouse
The marriage license window is in the County Clerk's office at 124 W. Beauregard in downtown San Angelo, a block off the old courthouse square. The office runs Monday through Friday, 7:30 in the morning to 4:15 in the afternoon, and stays open through lunch, but you'll want to come in before 4 p.m., because that's the cutoff for marriage licenses, probate filings, and occupational driver's licenses. Walk in at 4:10 and you'll be coming back tomorrow.
Both people need to show up together with valid photo ID. If one of you genuinely can't be there, whether deployed, hospitalized, or out of state, the clerk keeps an absent-applicant form on the county forms page that lets a license go through anyway, but it has to be filled out and notarized ahead of time.
Texas builds in a 72-hour wait between getting the license and the ceremony, so don't leave it for the morning of the wedding unless you've cleared the waiver (military members and a few others can skip it). The same clerk also handles informal-marriage (common-law) declarations and certified copies if you need proof later. Phone is 325-659-6551 if you want to check current fees before you drive in.
Source to confirm: Tom Green County - County Clerk