I had a few folks ask me about this and I suppose I could have used a little “how to” myself. So here is my version of “How to Organize a 5K.”
First and foremost, choose your location. The Lazy Runner and I found out the hard way that even once you decide on your location, the date for your race is entirely up to the location and it’s availability. The location is usually based on which governmental jurisdiction to work with, either a county or city. We used a local city park with a closed course because it was a whole lot cheaper than closing city roads which then require a lot of off duty officers. And closing roads ain’t cheap.

Our first choice for the date of our race was a whole month before the date we actually got. To be honest, I almost gave up with all of the back and forth we did with the City. LR kept us moving forward, he’s like a rocket ship in this regard. We were anxious to get the permits locked in so we could begin marketing. Obviously, it’s not a good idea to market your race without permits in place. 

I’d say the second most important thing in organizing a race is getting sponsors. Sponsors help cut that upfront cost you’ll have to pay for your permits. Get sponsors early and get as many as you can. Sponsors know that if they pick a popular race they’ll get tons of free press and show that they support a worthy cause and a healthy lifestyle. Again, get them soon and get as many as you can. 
Once you have your permits you can begin marketing. LR and I hit up every local running group we could find. We had postcards printed up and tagged cars at various races around the area. We used social media to it’s fullest extent and sent out emails to our list of runners. We also had a lot of word of mouth generated by friends and family. It helped that we are both locals and know a lot of people in the area.
While all of the marketing is happening this is when you will be seeing people register, we used active dot com since they are the most popular in our area. They also send the checks from the registrations weekly and that allowed us to purchase race items that we needed in order of importance. Again, sponsors offset a lot of the upfront costs while you are getting people registered. 
After the permits, the shirts seemed to be the costliest item on our budget. This is partially because I was a maniac about getting good quality shirts AND getting a cut specifically for the women. You’d be amazed at how quickly the shirt cost can add up and how fast people are to have issues with them. I fully understand wanting a nice race shirt that fits but now I also see it from the other side. This is why registering early is so important. It takes a lot of the guess work out of the ordering process when choosing sizes for shirts. The next time you get a shirt that is either too big or too small, think about when you ordered and when you picked it up. Things gets really crazy really fast the closer it is to race day. That being said, I did my best and will think twice before complaining at any races I sign up for in the future. 
Since LR and I are runners we were no way, no how, having a race without chip timing. I’ve run a few small races that use the card method. You know, you write down your time after you cross the finish line and go slap it into an age group card box? That method stinks and I personally like to see my time on the ‘puter and know it’s there for life, especially if it’s a PR. This was the second costliest item. It’s 100% worth it and most of the timing chip companies will set up the start and finish line and our let us rent a few tables and chairs that came in very handy. 
The park we used had bathrooms but since we were well over the number of runners we originally planned for we ordered three porta potties just to be on the safe side. I think that after the t-shirts, runners complain the most about potties. I know I do! 
Trophies, food, water, and race day stuff was ordered or bought last. Always buy more water and Gatorade or whatever beverages than you think you’ll need. People are thirsty! We had maybe 5 bottles of water left over and no Gatorades. The snacks for after the race don’t need to be big. We had chips, danishes, rice krispy treats, apples, and bananas. Skip the apples and get double bananas. I’ve been eating apples with every meal since Saturday. Heh. 
My biggest snafu was the damn safety pins. I was brain dead by the time I went to buy them and definitely didn’t purchase enough. Sonafab! However, most everyone was willing to accept my apology and share some pins on race day. Whew! 
Hosting a 5K is a lot of work. Don’t let anyone tell you otherwise. It may seem small in comparison to the big marathons and triathlons but remember, those are run by hundreds of people. And some of those people, it’s their only job! 
It was absolutely one of the most rewarding experiences of my life and I can’t wait to do it again. Please ask any questions you have in the comments. Ever thought of organizing one yourself?