There are several Geerin/Geren/Geurin/Garren families from NJ, SC and TN, some connect, some do not. My interest is tracking the ones who were in TN, Alabama and Texas before 1900--which ones connect and which do not. The Denton Co. Thomas E. Gerren/Gerrin/Garren/Geron is the "mystery" guy--most of the others can be tracked--he is not my missing Thomas and he is not with the Erath Co. famlies, or the Grayson Co., families--but he might be a cousin to Robert L. Geren who left TN for TX after 1880 and lived in Dallas and Denton counties.
For birth and death certificates in Texas after the state and counties began keeping track in the 1900's, there are too many gaps and misspellings on the forms and then the misspellings in the index. Besides several counties were not careful in keeping the records--example, one of mine died in Grayson Co. 1913--got the obit, but no death certificate; one of mine died in Stephens Co. 1960's, got some death information, his name is on the Texas state death index, but not available through the familysearch.org Texas death certificate images.
Tom was too young for the voter registration in 1867-68, so that leaves tax and possibly land records in Denton Co. to track Tom. He definitely married, had at least two children, a son and a daughter. He did travel all through north Texas and came into Indian Territory. He feuded with other officers, especially about Sam Bass; he did want the rewards for bringing in the alleged criminals; he was accused of faking evidence and 'setting up' a few boy/men to be killed while allegedly committing a crime; he had several critics of his methods; he still had a negative image among newspaper writers in Denton years after his death. He did work as a claims agent for the Santa Fe and got some folks very upset with his work---this is from1800's and 1900's news items. But one article only provided a date and location for his death in October 1912--no death certificate with any spelling variation, even with only first name searching. Guess this Tom will be a mystery.
For the 1860 census, there are a couple of possibilities, but nothing definite, and the 1860 census is incomplete for many areas in Texas, Arkansas, Missouri, etc, same with the 1870--got some who were definitely around these states, but did not show up on the census, even with page by page searching. Same problem with 1880, 1900, 1910, 1920--too many were missed and too many incorrectly indexed, but considering the spelling and handwriting on those old records, it's a wonder that what is available is even partially readable.