What appears to be a Glock 19 is seen being picked up by Cody Hoyt (Ryan Phillippe) in "Pilot" (S1E01).
Jenny Hoyt (Katheryn Winnick) carries one as her personal sidearm.
Sheriff William Tubb (William Gallagher) carries a 2nd Gen model as his duty sidearm in "Unfinished Business" (S1E04), but switches to a Glock 17 for the rest of the series.
Glock 17
Sheriff Deputies in the series are armed with the Glock 17, including Sheriff Tubb (William Gallagher).
In a continuity error, Rick Legarski's SIG-Sauer P226R turns into a Glock 17 in "A Good Day to Die" (S1E05).
Glock 18C
A thug in "Catastrophic Thinking" (S1E10) is armed with a Glock 18C with a stainless slide, probably an airsoft model made by WE Tech.
Glock 26
Jerrie Kennedy (Jesse James Keitel) owns and carries a Glock 26 as her personal handgun. She first uses it in "Bitter Roots" (S1E15).
SIG-Sauer P226R
Montana State Trooper Rick Legarski (John Carroll Lynch) carries a SIG-Sauer P226R as his duty sidearm.
Some Troopers also carry P226Rs throughout the series.
U.S. Marshal Mark Lindor (Omar Metwally) uses one as his duty handgun, although after "White Lion" (S1E13) it changes to a SIG-Sauer P229R.
SIG-Sauer P229R
US Marshal Lindor (Omar Metwally) starts carrying a P229R as his sidearm in "White Lion" (S1E13).
SIG-Sauer P228
In a continuity error, Lindor's SIG-Sauer P229R turns into a P228 when he enters a house searching for Pergman in "Love is a Strange and Dangerous Thing" (S1E16).
Walther P88 Compact
Cassie Dewell (Kylie Bunbury) carries a stainless Walther P88 Compact with wooden grips as her personal sidearm throughout the season.
Beretta PX4 Storm
Starting from "The End is Near" (S1E08) Jenny Hoyt (Katheryn Winnick) carries a Beretta Px4 Storm as her personal sidearm.
John Wayne Kleinsasser (Kyle Schmid) takes it and uses it to threaten Jenny in "Bitter Roots" (S1E15).
Horst Kleinsasser (Ted Levine) draws and discharges a Charter Arms Bulldog in "All Kinds of Snakes" (S1E11).
Cheyenne Kleinsasser (Britt Robertson) uses one in "Bitter Roots" (S1E15).
Various Revolvers
Attendants at Cody Hoyt's funeral shoot commemorative blank rounds in the sky with various double-action revolvers in "The Wolves Are Always Out For Blood" (S1E06).
Submachine Guns
Heckler & Koch MP5A3
Sheriff Deputies and SWAT Officers are armed with Heckler & Koch MP5A3s during the raid on Ronald Pergman's (Brian Geraghty) house in "Let It Be Him" (S1E09).
Shotguns
Double Barrel Shotgun
A side by side double barrel shotgun with hammers is used by Ronald Pergman (Brian Geraghty) to set up a booby trap on his front door in "Let It Be Him" (S1E09).]]
Remington 870
John Wayne Kleinsasser (Kyle Schmid) uses a Remington 870 with wooden furniture in "No Better Than Dogs" (S1E12).
Rosie Amaya (Michelle Veintimilla) also owns one to defend her cabin.
Rifles
M4A1 Carbine
Sheriff Deputies, Montana State Troopers and SWAT officers are armed with M4A1 Carbines during the raid in "Let It Be Him" (S1E09).