City of Houston public safety (Police and Fire/EMS) and other government services operate on the TxWARN system. Public Safety primarily uses the "Houston Public Safety" sites and government services use the "Houston General Government Services" site. However, there are exceptions, particularly for interoperability. The Aviation Department operates on the Harris County sites.
Harris County operates a wide-area trunked radio system known as the Texas Wide Area Radio Network (TxWARN) that is used by Harris County agencies as well as many other agencies in the greater Houston metropolitan area. In addition to radioreference.com, KG5AI has an Excel file of talkgroups.