The closest dojo I know of is about 14 miles from McKinney. It is about 1/2 way to Dallas, if I remember the area correctly. Anywho, the name of the place is Plano Aikido Center, and it's location is 1445 Los Rios Blvd. #101, Plano TX 75074. The chief instructor is Sidney Shiba. Look him up if you are interested.
This is about 22 miles away, about 40 minute drive as well.
It seems all the places favor close proximity to Dallas. It's too bad because in McKinney alone there is 125,000+ people not counting Frisco which is next to McKinney which also has no listed places.
I heard someone talking that they saw/heard of an Aikido Sensei in McKinney with a small group. But, I've not found any.