Old track is out NE of the Airport by Soi Jintakan. I have no idea of when they might race there..
New track is 3km past Big C just south of the Sakhon Nakhon highway.. Go past the loop road Big C intersection (the unfinished flyover), drive past the 7-11, then the Border patrol Police Camp (you'll see the old C-54 hanging over the wall), then the turn to the Sanam Maa will be the 2nd break in the median.. You have to drive against traffic 20 meters and then south down a concrete road about 600 meters to the horse racing track.. The races are genearlly on Sundays unless that particular Sunday is a Wan Pra and then the races will be on Saturday...
there are some other threads on the track with tips on betting too...
You can see both tracks if you go to Google Map and do the sat view of Udon..
races used to be on saturday, and no need to drive against traffic, go a bit further for a u-turn, if memory serves. they are interesting for one time, not a big horse race fan, although used to go with brother occasionally in states and actually handicap them and bet. here i was a bit surprised, up the first time, not knowing much, then realized it was pretty obvious something was up.