You could do it that way, if you want. Just remember that your scanning speed will take a hit, since you are using the same system twice, once in each Favorites list. It takes the one to one & a half seconds for each trunked system, for it to find and decode the control channel data, and then look to see if any of the programmed talkgroups are active. While you would be scanning the same system, by dividing it into two, one with Sheriff's talk groups, the other with everything else, it is still treated as being two systems, since each part is on a separate Favorites list.
You could also do the division by departments, in just one system. One department with S.O. talkgroups, others for other categories (fire, ems or whatever). Instead of turning a favorites list off, to concentrate on just one category, you can, instead, have both categories on the same list, but turn the respective departments on or off as desired.
If this one system is the main thing you are listening to (on that scanner), then you may not notice (or, at least, not mind) the slightly slower scanning. Are you programming in all four sites for the
system? Or just the one for your county?