Welcome to Radio Reference.
Lapeer Co. is on the MPSCS(Michigan Public Safety Communications System). Your scanner is capable of receiving this P25 system as it is still in Phase 1.
If you go to the top of the page here click on the "Database" button. On the map click on Michigan. This will bring up a map of Michigan with all of the counties. Click on Lapeer Co. and on that page, scroll to the bottom, where it shows "All trunked radio systems in Lapeer County". Then click on "Michigan Public Safety Communications System"
On this page scroll down to "System Frequencies" and scroll down a little further to 2(2) 025(19) which is the Lapeer Co. Simulcast. The blue frequencies are the alternate control frequencies and the red frequency is the main control frequency. These are the frequencies you will want to program into your scanner.
If you scroll down a little more on this page you will get to the "System Talkgroup" section. Now you will have to scroll down some more to State Police District 3 Talkgroups. These talkgroups will cover your State Police district. Then you will have to scroll down quite a ways down until the counties will show up in alphabetical order. Scroll down and there will be 5 sections of Lapeer Co. talkgroups(police, fire, etc.) that you can select to program into your scanner.
I own Uniden scanners and haven't programmed a Whistler type scanner in 7 or 8 years so maybe someone else on here can chime in on programming help if you need some. Also simulcast systems can be a little tough on you scanner. Depending on your location in Lapeer County your reception may seem choppy and broken up due to multipath distortion.
There is also a Michigan Radio Discussion Forum to help with local questions.
Good luck and have fun.
Jim