World's Largest Races
The Peachtree 10k, held on July 4 in Atlanta, Georgia, is the world's largest race, according to Running USA's Road Race Information Center, with 52,393 finishers. The Bolder Boulder 10k, in Boulder, Colorado, ranks 2nd in the USA and 6th in the world with 42,391. Lilac Bloomsday 12k, in Spokane, Washington is right behind in 7th place, attracting 40,012 runners.
Don't let these stratospheric numbers influence your race planning, though. More than half of the thousands of American races produced each year tally less than 300 finishers. If you are trying to increase the size of your small, community race, expect incremental growth.
The megaraces of the world have taken years to build up and draw on vast sums of money, considerable marketing and public relations resources, and popular locations (OK, maybe not in the case of Spokane).
So, be realistic, set achievable goals, and do the best you can with the resources you have.