O3 Apothecary is listed with downtown McKinney's health and beauty businesses, one of the shops on West Louisiana Street a short way from the square.
It is at 201 West Louisiana Street, in the 200 block of West Louisiana, at D15 on the printed downtown map. Downtown Dry Goods, McKinney Knittery and Pavitra Organic Day Spa are nearby on Main Street's list, so it fits easily into a walk along West Louisiana. Parking in the district is free.