When I graduated the Academy in 2002 my first purchase was a Beretta 92 Compact Type M Inox from the LAPD Academy store (LAPRAAC) I already had several Berettas and that one seemed cool and unique. Soon after that I picked up a S&W 4506 because it fit my hand better than the HK USP we authorized.
LASD had similar pistol requirements as LAPD for some time. The Beretta 92F series was issued by LASD from the late 1980s until 2010. After the North Hollywood Shootout in 1997, LAPD and LASD both authorized personal purchase of certain .45 ACP pistols. LAPD authorized the S&W 3rd gen guns as well as the Beretta 8045 with the 4" barrel (LAPD model). LASD authorized Smiths and Berettas but also authorized the HK USP45 and the Ruger P90. Some deputies bought the LAPD model 8045 (or the regular model) and used them on duty but the HK USP was far more popular than any of the other options.
In late 2002 to early 2003 LASD authorized the Crimson Trace Lasergrips for duty use. I was in the second class in February 2003. Lasers are still authorized to include light/laser units like the Streamlight TLR-2 series and Surefire X400, but internal lasers like the Lasermax are prohibited.
In 2003 (I think) LAPD switched to Glock 22s for issue to recruits (as has been mentioned by people who know more than me - in LAPD you keep what they issue you and if you want to carry something else you have to buy it.). At some point LAPD SWAT, who had been carrying 1911s of various flavors (many of them confiscated crime guns to my understanding) went to Kimber. Later SIS went to Kimber as well. Around 2010-2011, LAPD began to allow regular officers who qualified "expert" to carry 1911s after completing the 3-day class and around that time I think they also switched to the Glock 17 instead of the 22 for issue to recruits, but it may have been a bit later.
In 2005 the LASD authorized the HK P2000 9mm as a personal purchase pistol and allowed recruits who wanted to purchase the pistol and holster to use it in the academy. This was in response to complaints about the size of the Beretta's grip for small-handed people. There had been a previous policy that if one couldn't work a full-size 92F/FS they could be issued aw 92FS Compact Type M in the academy, but then they would be prohibited from carrying the full size pistol (and be stuck with 8rd mags). Authorization of the P2000 opened the door for the potential of other options. Until that point LASD had been adamant that a duty gun must have a manual safety - that had been one of the biggest, if not the biggest selling point of the Beretta to Sheriff Sherman Block back in the 80's and it stuck - LASD still (to this day) mandates that if a handgun has a safety, it is to be carried with the safety "on".
I think it was around 2007 that CHP started switching out their old S&W 4006s for the new CHP 4006TSW with the light rail as part of the frame (as opposed to the riveted rails on other TSW models).
In 2007-2008 LASD began looking at the S&W M&P and Sig pistols. Sigs (the P226 and P229 in 9mm and P220 .45) were approved first in late 2008 or 2009. The M&P was approved soon after and M&Ps were issued to an academy class. Those M&Ps were famously (infamously) pulled from service and prohibited as personal weapons when the academy class experienced a large number of malfunctions. What wasn't publicized was that the malfunctions continued with the Berettas that replaced the M&Ps and it was later determined that bad ammunition was a partial cause of the reliability issues. That said, S&W did find a problem in the manufacture of the extractors in that batch of pistols and after confirmation testing that the problem had been resolved the M&P was re-authorized.
LASD began issuing the M&P to recruits formally in late 2010 to early 2011. This continued with the exception of some classes in 2012. They were issued Berettas because the Department ran out of M&Ps in inventory. In 2019 recruits began to be issued the M&P9 M2.0.
In late 2012 LASD approved a department-wide optional conversion to the M&P. This led to the increase in unintentional (largely negligent) discharges that was highly publicized. I don't always agree with LAPD policy, but there's something to be said about how they issue guns to new recruits without converting the whole department. Eventually LASD got a handle on the UD issue. There are now few Berettas left in the field but there is a cult following among a small group with the Wilson Brigadier Tactical and Langdon LTT models being popular.
In 2014, around the time that LASD authorized the S&W Shield for backup and off duty, LAPD started issuing the M&P to recruits. By this time we'd become friends with several of the LAPD firearms staff, including one guy who had been a deputy when I started - I was in the academy with his wife, and he was one of the first guys I worked with and my inspiration to pick up that first S&W 4506. We competed against each other frequently in the SoCal LE shooting matches like the Special Forces benefit match, All State Steel Challenge, and the LEAAP match. In recent years there had been talk about LAPD updating to the M2.0 for recruits but I wasn't aware if they actually made the switch. From what has been said in this thread it sounds like they did.
Through some cooperation with the Special Enforcement Bureau who wanted to carry "G" model Berettas - The Wilson Combat Brigadier Tactical to be specific, the LASD authorized list was expanded significantly by authorizing "families" of handguns. This authorized the "G" model Berettas, most of the Sig "classic" series in 9mm and .45, and 9mm as well as .45 USPs, P30s, and HK45s.
A new LA County Sheriff was elected in 2014 and took office in December. He came from LAPD and Long Beach, both of which authorized 1911s and within a week we had a call from "executives" asking if we'd looked at 1911s. Thankfully we'd spent the last six months putting together a proposal. Several of us took the LAPD 3-day 1911 class. This morphed into a large package of firearm proposals that ultimately resulted in the August 2016 authorization of 1911s (ten manufacturers) for those who could qualify expert, Glocks in 9mm and .45 for those who had been through the M&P conversion training, and .380s for off-duty and backup use.
In 2019 LASD authorized the Sig P365, Beretta PX4, and Kahr K9 for off-duty/backup and the STI to be added to authorized 1911 manufacturers. I think LAPD beat LASD to the STI by a few months.
Unlike in LAPD, where the 1911 has a strong (and cool) history, the 1911 is not very popular and there are probably less than 150 deputies certified to carry them.
In 2018, after years of trying to get the Department to look at pistol optics we managed to get permission to start evaluating them. In the midst of this LAPD started looking heavily at optics and that helped the LASD break through some supervisorial hurdles to the project. We began a collaboration with LAPD. In January 2020 LASD approved pistol-mounted optics for deputies who could qualify as an "expert". The optics that were authorized were those which passed the LAPD formal testing. LAPD had some unfortunate delays in the approval process due to their initial push to issue them to an academy class, COVID, riots and de-funding, but it's my understanding that optics were recently approved by LAPD for personal purchase/use.
LAPD SWAT has moved away from Kimber now but I think they still authorize them. They have also authorized some additional manufacturers of 1911 handguns and according to some recent training we did with their SWAT guys is in the process of fielding Sig 1911s. I can't say across the board but the two guys I talked to were not very happy with them.
For both LAPD and LASD training classes are required to carry different pistols than what is issued but there are differences in the details of the classes and qualification requirements.
CHP did go to the M&P a few years ago and stuck with the 1.0 in .40 because they have a long history with the .40 and, as was mentioned earlier, they wanted to go with the proven design rather than the new 2.0. I also think that for a while they had a personal purchase program for patrol rifles but I think they ended that several years ago.
LAPD has a personal patrol rifle and personal shotgun program which is pretty cool. LASD does not. LASD issues a semi-auto Colt (14.5" bbl) or FN (16" bbl) M4 with an Aimpoint H-2 and a couple different WML options. LASD is actively looking at options for a better WML for the issued rifles. Not sure how this will pan out with the budget being what it is but if nothing else I'm hoping for individual deputies to be able to purchase a better light. LASD shotguns are pool guns. Remington 14" bbl 870s with Knoxx stocks, Mesa sidesaddles and older Surefire WML forends.
That's my rambling rundown of most of what I know about LASD, LAPD, and CHP firearm stuff. Crazy to think I started my law enforcement career being issued a used Beretta 92FS to now running Glocks and M&Ps with optics and WMLs.