At over 65,000 square miles it was half the size of New Mexico. That's because it was, in fact, the Eastern half of New Mexico.
It was Santa Fee County, created in 1848 by a proclamation of Governor George T. Wood.
But just proclaiming something don't make it so, unless you're prepared to back it up. There was a major problem for the governor. I know this is hard to believe, but the people living there did not want to be Texans.
They were against slavery, and besides that, they still resented the attempts to invade them that had been made over the years (Texas saw this as 'establishing jurisdiction'.)
In 1849 there was a new sheriff in town, or to be less cliche and more accurate, a new governor assumed office.
Peter H. Bell was a veteran of the Texas Revolution. He had been a private in Captain Karnes spy/cavalry company. He fought in the Battle of San Jacinto, fought Indians as a Texas Ranger, and commanded a Ranger company under Zachary Taylor during the Mexican War.
He proposed to 'establish jurisdiction' by force and he was just the man to do it.
But like most things, it eventually came down to money. Debt is a bad thing and Texas had a lot of it left over from her days as a republic.
In return for paying off $10 million of the former Lone Star Republic's debt, Texas gave up to the Federal Government not only her claim to the Eastern half of New Mexico, but also a third of Colorado, as well as portions of Kansas, Oklahoma and Wyoming. That's about twelve cents and acre.
They called it the Compromise of 1850.
If it weren't for those big, fat public debts, Las Cruces, Albuquerque, Santa Fe and Taos might be part of Texas today.