The Federal Communications Commission has officially announced the beginning of the national rollout of the long-planned Text-to-911 service. The federal regulator has launched a dedicated site regarding how the rollout will work, with the goal of eventually covering the entire country through all four major carriers.
However, the actual service and capability is only available in select US states and counties at this time, with all four wireless carriers pledging to speed up the nationwide rollout, first by rolling out bounce back messages for those that attempt to use the service in an area that has not launched the service as of last year, and subsequently working with states and counties to speed up availability as soon as possible aside from rolling out nationwide access.
The current rules allow for individual 911 dispatch centers to make the final call on whether to accept emergency 911 texts regardless of readiness, which means that the goal of nationwide coverage is ultimately up to county dispatch centers as there is no hard mandate for immediate support, nor is there a set date for complete nationwide coverage. Below, a linked PDF detailing which states and counties currently support Text-to-911 capability.