Texas probate venue is set by where the decedent had a fixed place of residence at death, not by where the estate's most valuable property sits. One county takes the entire estate, real property included.

A small group of large counties, including Harris, Dallas, Bexar, Tarrant and Travis, have dedicated probate benches. Those judges hear probate, guardianship and trust matters exclusively.
The first decision in a Texas probate is not which kind of administration to ask for. It is which building to walk into, and that answer is set by statute rather than convenience. People assume the filing follows the land, because the land is the valuable thing and the land is what the family argues about. It does not. Venue follows the person who died, and a careful reader works that out before paying a filing fee in the wrong county and starting over three weeks later.
Texas Estates Code venue rules point first to the county where the decedent had a domicile or fixed place of residence, and that single county takes the whole estate, including real property sitting hundreds of miles away. A woman who lived in a Fort Worth apartment for eleven years and owned two hundred inherited acres in a rural county is probated in Tarrant County. If the decedent had no fixed residence in the state, the rules move to the county where the principal property was located at death, or the county where death occurred, in that order. The distinction that trips people is between residence and sentiment: the family homeplace, the mailing address used on hunting leases, and the county named in the will are not venue facts.
The out-of-county land is handled after the fact, not by a second probate. Once the will is admitted and the order signed, a certified copy of the will and the order goes to the county clerk where the land lies, to be recorded in the real property records of that county. That recording is what a title company will look for when the buyer's lender asks how the property left the decedent's name. It costs a recording fee and a certified copy fee, and it is easy to forget for two years until a sale falls out of contract over it.
Which court hears the case depends entirely on the county's size and structure. A small number of populous counties, Harris, Dallas, Bexar, Tarrant, Travis and a handful of others, have statutory probate courts: dedicated benches that hear probate, guardianship, and trust matters all day and nothing else. A second tier of counties routes probate to a county court at law, where the judge is a lawyer but also carries misdemeanors, civil cases, and family matters. Everywhere else, the constitutional county judge hears probate, and that judge is an elected county administrator who is not required to be an attorney.
The practical difference shows up in contested matters and in how fast an uncontested application moves. In a statutory probate court, a will contest stays put and gets tried by a specialist. Before a constitutional county judge, a contested proceeding is typically transferred to a district court or heard by a statutory probate judge assigned to sit, which adds weeks. Uncontested filings often move faster in the smaller counties, because the docket is shorter and the judge may hear prove-up testimony the same morning you appear.
Clerks do not evaluate the merits, but they do reject filings on form, and the rejections are predictable. The original will, ink signature and all, is required for a standard probate; a photocopy sends you into a separate and slower proceeding to prove a lost will. The application itself must be sworn, must name the decedent, the date and place of death, the county of domicile with facts showing venue, and must state whether children were born or adopted after the will, whether the decedent was ever divorced, and whether a child support lien exists against the estate. Filing fees are due at submission. Most counties in practice will not open an estate for an unrepresented applicant seeking letters, because acting for an estate is representing someone other than yourself.
Call the clerk's office in the county of domicile and ask three narrow things: which court number takes probate, what the current filing fee is, and whether the court requires a proposed order submitted with the application. Confirm the four-year window has not run since death, since that closes the ordinary route to letters testamentary. Have the death certificate, though not every county requires it at filing. Once letters issue, the estate needs its own taxpayer identification number from the IRS, which oversees estate and fiduciary income tax filings, before a bank will open an estate account.
Getting the county right on day one costs one phone call. Getting it wrong costs the fee, the wait, and the small indignity of explaining to the beneficiaries why the hearing everyone took off work for is not happening.