Normally in Texas, most judges will put a residency restriction on the party that has primary custody of the kids.
It is normally the county they currently live in and any county contiguous to that county.
Contiguous means that it "touches" the county.
So for Harris County that would include Montgomery, Ft. Bend, Waller, Chambers, Liberty, Brazoria and Galveston counties.
And Ft. Bend surrounding counties would be different then Harris County and surrounding counties. The surrounding counties for Ft. Bend would be Wharton, Austin, Brazoria, Harris and Waller counties.
Of course, this area is huge so I usually find that it does not work and if agreed by the parties then the area can be limited - say to one county or to even a school district or a geographic area in a city (such as zip code 77024).
It is easier to co-parent and see the kids when you live close together.
Let's be realistic, kids forget their "stuff" all the time and it's much easier to stop by the other parent's home to get the forgotten time when you live nearby versus an hour away.