Approximate population of Texas 1836 - 30,000
1842 - 100,000
1850 - 200,00
1860 - 600,000
1870 - 800,000
Last major Indian War being the Red River War of 1874.
The point being, only a minority of residents at any given time lived within the reach of Indian raids, the proportion of those who did steadily decreasing as the population boomed and the settlement line moved west. Figure slaves were about 25% of the whole, at least at one point in time, so multiply the above numbers by 0.75 to get an estimate of the Anglo population.
Back when women were still having kids the rule of thumb was 20% of the population would be active men and youths of combat age. So in 1836 this estimate would be 4,500 White men and youths, 1842 - 15,000 White men and youths... etc. A good number of these in 1836 were involved in the events of the Texas Revolution, especially when Santa Anna's columns moved into East Texas subsequent to the Alamo.
Other than that, if 100 guys were actively involved in the field against Indians at any given point in time during that whole 40 years, that was a lot. Being a Texas Ranger was expensive, dangerous work and few men cared for it.
OTOH, in the early years of Texas, the threat of a Mexican invasion was very real. If nothing else the fact that upon independence the new Republic of Texas had unilaterally presumed to annex a 150 mile-wide strip of land between Corpus Christi and the Rio Grande, land that was at that time part of the Mexican States of Taumalipas and Coahuila, guaranteed there would be problems.
The Mexican Civil War over the Constitution of 1824 that Santa Anna kicked off when he abolished it in 1835 would not be over in Mexico until 1840. Meanwhile, the government of the pro-Constitution Federalista side was actually given uneasy sanctuary in Texas, the seat of the Federalista government in exile being Victoria TX, and the Federalista arsenal being located in Linnville TX on the Gulf Coast. Much of the muscle for the Federalista side here was supplied by the mercenary Texian Reuben Ross and his band of 200 outlaws.
Reuben Ross was apparently not a nice guy and among other things instigated frequent duels. In 1839 he crippled the arm of famed Texas Ranger Ben McCullough in such a duel and subsequently demanded a rematch to finish the deal, whereupon Ben's older and somewhat less-famous brother Henry shot down Ross in Gonzales under poorly-recorded circumstances. A pity, there was likely a good story there.
When the Constitution War ended in 1840, some of the defeated Federalista elements would attempt a short lived Republic of the Rio Grande, incorporating the states of Northern Mexico including what is present-day Texas south of Corpus Christi. As conceived, the Republic of the Rio Grande would have immediately been in conflict with Texas over real estate. Nevertheless the Republic of Texas President Mirabeau Lamar, seeking a buffer State between Mexico and Texas, supplied arms and ammunition and actively encouraged Texans to take up arms to support the cause. More than 400 did, which was a very large number at that place and time. Didn't work though and the project failed within the year.
The threat from Mexico was not an idle one, everybody knows a Mexican Army took the Alamo in 1836, most people don't know that a 1,500 man Mexican Army, under orders from El Presidente Santa Anna himself, would take San Antonio and the Alamo all over again in 1842. Didn't stick, in 1836 there were 30,000 Americans in Texas and that was too many, in 1842 there were 100,000.
Ironically, this second Mexican invasion would be a major catalyst in overcoming the widespread Northern opposition to the annexation of Texas into the Union, that 1845 event precipitating the Mexican War.
Meanwhile, throughout this whole period, Mexican government agents were actively fermenting unrest among the Indians in Texas, including probably the Comanches as events turned out.
