|Name||William "Will" LaMontagne, Jr.|
|Family|| Detective William LaMontagne, Sr. (father; deceased)|
Jennifer Jareau (wife)
Henry LaMontagne (son)
Sandy Jareau (mother-in-law)
Rosaline Jareau (sister-in-law; deceased)
Unnamed father-in-law (deceased)
|Occupation|| New Orleans Police Department detective (former)|
D.C. Metropolitan Police Department detective (current)
|Portrayed By||Josh Stewart|
Will was first seen in Jones as a New Orleans detective investigating a serial killer case which had initially belonged to his father, a detective who had been killed during Hurricane Katrina. The killer was believed to have suffered the same fate, but when evidence to the contrary arose, Will took over the case using the work his father had done (and a single word carved on the wall of his father's home). Will eventually called in the BAU to assist him and they were ultimately successful in capturing the murderer. During the case, he and JJ are seen to develop an attraction towards each other.
Will reappears in In Heat, where it is revealed that he has been romantically involved with JJ for over a year and in The Crossing we discover JJ is pregnant; in the Season Three finale Lo-Fi, William tells JJ that he is willing to give up his job in New Orleans to raise the baby with JJ. He has also asked her to marry him, to which she said no.
As the BAU attempt to track down George Foyet in 100, he and JJ take Henry to a pharmacy, where JJ finds out an important clue in the case. The clue helps the BAU find Foyet's address in Washington D.C., but they find him gone. After Hotch's ex-wife Haley is killed by Foyet, Will is one of those attending her funeral in The Slave of Duty, where he offers Hotch his condolences.
In There's No Place Like Home, Will and JJ are taking care of a sick Henry when she gets called into work. They start an argument it's clear they've had before. Will is unhappy with JJ's job and wishes she still worked at the Pentagon so she could have nights and weekends off. She offers to stay home but he tells her to go. While presenting the profile of a killer who strikes during tornadoes, Will calls and sends her text messages about an emergency concering Henry. When she calls him back, Will tells her that he's at the hospital with because Henry's had a seizure. She makes plans to leave immediately but the weather has grounded all flights. She finishes the case and the episode ends with Will putting her on speaker phone so the two of them can read Henry a story at bedtime.
Will plays a major role in the two-part season finale Hit and Run, where it is revealed that he is still a detective, but now works with the D.C. Police, when he shoots Oliver Stratton after his partner is killed by him, earning him the hatred of Oliver's brother Chris. During a hostage situation at a bank, Chris asks for Will to enter the building. Feeling he is responsible for the deaths at the bank, Will accepts the call despite JJ's protests and calmly walks inside the bank, confronting Chris, who asks him his name. When Will states his name, Chris promptly shoots him twice. While a bulletproof vest protected him from one of the bullets, Will was hit in the shoulder and critically injured. He is treated by two hostages before confronting Chris again, telling him that his partner was secretly planning behind his back. To convince him, Chris takes him to the gas lines, where they find the female unsub (whose name we eventually find out is Izzy) setting a bomb. The bomb detonates, allowing Chris and Izzy to flee with Will as a hostage.
Chris and Izzy later force a medic at gunpoint to mend Will's wound before the latter kills the medic, and eventually Chris. Izzy then picks up Matthew Downs, a former Marine who happened to be one of the hostages treating Will's wound at the bank. They go to Will and JJ's house, where they find Henry under the watch of a neighbor. Will, being forced to be compliant, convinces the neighbor that Izzy is his cousin and that she will be babysitting Henry before leaving with Matthew, who takes him to Union Station. All the while, Downs rants on about how disconnected from the world he felt after serving several tours as a U.S. Marine. The two stop at Union Station; Matthew takes Will to a bathroom and straps a bomb onto him, intending to detonate it and kill Will and anyone else still in the building. However, he is found by the Prentiss and she successfully defuses the bomb, while Matthew is shot and killed and Izzy is arrested before she can do any harm to Henry. At her request, Will proposes to JJ again and the two are married by the end of the episode.
Season Eight Edit
Will reappears in Nanny Dearest, where he is once again left with Henry when JJ leaves to investigate a case. When JJ returns home after closing the case, she greets him with a passionate kiss that surprises him. The two take a look at a sleeping Henry before JJ closes the door to his bedroom.