Is it legal for Texas to pass a law that only applies to Harris county?

How is it legal for Texas a law that only applies to counties with more than 3.3 million people?. It would apply to only 1 out of 254 counties.

https://www.texastribune.org/2025/08/27/harris-county-constables-contracts-bill/

Harris County constables, sheriffs could contract with HOAs without commissioners’ OK under bill heading to Abbott

Currently, sheriffs and constables in Harris County can contract with homeowner associations, school districts and municipal utility districts to provide additional policing for them. Both the county and contracting groups have to sign off on the contract, and they split portions of the cost depending on the amount of time the deputies spend in the area.

The more prominent of the two proposals, House Bill 26, would allow these law enforcement agencies to enter into such contracts without the need for approval from the county’s commissioners court. Meanwhile, House Bill 192 would require the county to seek voter approval if it adopts a budget that reallocates unspent funding that was appropriated for law enforcement agencies or moves funding previously appropriated for a specific law enforcement position to another agency.