Back in 2016, TxDOT supposedly decommissioned all of FM 426 at the City of Denton's request, so the city could widen the road. However, today, I found this map from the City of Denton on Facebook https://www.facebook.com/photo/?fbid=532148378942315&set=a.223040436519779 (https://www.facebook.com/photo/?fbid=532148378942315&set=a.223040436519779). It shows that a tiny segment of FM 426 is still state maintained. This segment is from the eastern city limits of Denton, east to the end of FM 426. The highway designation file says that the entire route was removed from the state highway system, but, in the same entry, says that the decommissioning only goes east to the eastern city limits of Denton. The minute order backs this up. Google street view shows that the route marker signs on the remaining segment have been replaced. I remember that the END 426 1000FT was previously brown due to aging. However, there is also a signage change that contradicts this. The county removed their county maintenance begins/ends signs at the ends of the roads that serve the trailer park back when the decommissioning took place. I'm wondering what happened, whether the fact that a segment was outside the city limits was overlooked by TxDOT at the time of decommissioning, or if the county flat-out refused to take over the remaining portion of the road.
Another issue related to this was back when the decommissioning first took place. The decommissioning was done with two separate minute orders, one for the section west of SL 288, and another for the section east of SL 288. At this time TxDOT removed signage from the portion west of SL 288, and change the signs on SL 288 from goalposts to straight posts that read " EAST 426 --->" and <---EAST 426. So, it looks like at that time, the sign crew only got one of the two minute orders.
Highway Designation File:http://www.dot.state.tx.us/tpp/hwy/fm/fm0426.htm (http://www.dot.state.tx.us/tpp/hwy/fm/fm0426.htm)
Minute Order:https://publicdocs.txdot.gov/minord/MinuteOrderDocLib/114635.pdf (https://publicdocs.txdot.gov/minord/MinuteOrderDocLib/114635.pdf)
https://www.txdot.gov/apps/statewide_mapping/StatewidePlanningMap.html agrees (click Control Sections at left).