Important notice: Crossbows are lawful for any person during the Archery-Only Open Season in all counties except Collin, Dallas, Grayson and Rockwall counties, where no person may use a crossbow to hunt deer during the Archery-Only Open Season (Sept. 27 - Oct. 31) unless the person has an upper-limb disability and has in immediate possession a physician's statement that certifies the extent of the disability. An upper-limb disability is a permanent loss of the use of fingers, hand, or arm in a manner that renders the person incapable of using a longbow, compound bow, or recurved bow.
Any person, regardless of physical ability, may use a crossbow to hunt game animals or game birds in any county, including Collin, Dallas, Grayson and Rockwall counties, during a general open season or Eastern spring turkey season.
An archery stamp endorsement is required to hunt deer during the Archery-Only Open Season. An archery stamp endorsement is required to hunt deer at any time in Collin, Dallas, Grayson and Rockwall counties, including during the general open season (Nov.1 - Jan.4).
A crossbow is lawful for game animals and game birds, provided:
the crossbow has a minimum pull of 125 pounds;
the crossbow has a mechanical safety; and
the crossbow stock is not less than 25 inches in length.
Telescopic sights are lawful.
Projectiles (Arrows and Crossbow Bolts):
While hunting game animals and game birds, a projectile may not be poisoned, drugged, or explosive.
When used to hunt turkey and all game animals other than squirrels, a projectile must be equipped with a broadhead hunting point that is at least 7/8-inch in width (upon impact) and has a minimum of two cutting edges. A mechanical broadhead must begin to open upon impact and, when open, must be a minimum of 7/8-inch in width.
An archer may have arrows/bolts with field, target, or judo points in the quiver with the broadhead hunting points.
This is a cut and paste from: http://tpwd.texas.gov/regulations/outdoor-annual/hunting/general-regulations/means-and-methods