I think every homeschooling family has heard this question about a hundred times in various ways.
So here's the four main places/ways that we meet friends:
1. Enrichment Classes
We're fortunate to be enrolled in a charter school. That means the school pays for any enrichment classes that we take. This is a big deal for me and frankly one reason that I decided to homeschool; in our current financial state, we cannot personally provide things like sports teams and music classes to our children, and we thought those are important opportunities.
So far the girls have done theatre class with other homeschoolers and gymnastics and ballet with a mix of children. Next year they will do theatre again as well as roller skate lessons, gymnastics again, and probably soccer or basketball for Primus.
They haven't thus far made any lasting friendships through these activities (mostly because I have not personally connected with any of the parents), but it has been good for them to associate with and have fun with a wide variety of children of all ages.
We are active in our religion. That includes two hours of Primary (Sunday school for ages 18 months-11 years) every single Sunday. These associations and friendships are very important. There are also a few families that we have met through church that also homeschool. So we get together with them at a park once a week.
3. Random (Providential) Encounters
Last summer I met a friend of mine at a local park one day to play. There happened to be another mom there with five kids in tow that were very similar ages to our own children. My friend, being the super out-going and not shy type went right up to that mom and said, "You have a big family! I love big families! I have three children and plan to have more. Big families are kind of rare these days. Your children are beautiful! What are their names? We'll be here again next week, want to join us?"
As it turned out, that mom is a homeschooler and has become one of my closest friends. Our kids all get along great, too. We now get together once or twice every week.
Meetup.com is a free site for individuals to sign up for, however some of the groups do ask a small fee from their members to cover what the site charges them.
I found a couple local-ish homeschool communities on this site and picked one that really fit us well. They get together every Friday, usually at a park, to play and do an activity. (It's usually about a 20 minute drive for us, so we only go about once a month.) It could be arts and crafts, sports, science projects, show-and-tell, or service projects. They also plan holiday parties and various extra activities and field trips.
We've been a part of this group for just over a year and have formed some great friendships with a few families.
Homeschoolers have to be more proactive when it comes to finding a community and building friendships. But it's so worth it!