Where are you in the US, which state? I agree with several posters that workplace colleagues are not always 'friends' material.
Is it a big firm/company you work for?
Until I know your state, it's hard to make a cultural comment (I'm from NH/Maine). But finding organisations outside of work is more likely to offer opportunities to meet like-minded people as suggested.
I was single until age 44 and lived in a New England seaside town about the size of Penzance. It was hard to meet other people once I left the university job and became self-employed. At uni job, my colleagues were my friends. So when I got home, I didn't feel a need to socialise and had quiet evenings in, happy with my own company.
Once my self-employment work started to get really busy, my customers became great social friends, but not ones I felt really close to for confidences, etc. It was also very difficult to meet eligible men as it was more of a family town for the locals. But lots of tourists in summer... more families!
Actually, I met my husband when travelling around the UK and popped into a pub. He just happened to be there and after talking for 3 hours, we knew we wanted to see more of each other. Within a year we were married and we first lived here in the UK, then he got early retirement and we moved back to the US for 8 years, then we left again and moved back here to the UK. Felt a bit like a yoyo LOL. But we have not been here 16 years and I think here in the UK there are more things for older single people to do. EG coach trips, Univ of 3rd Age, National Trust volunteering, and community volunteering. Or church, if you are spiritual.
Depends on your interests. And with the internet, it should be possible to find things in your area, or within driving distance. Give it a go... and if you are OK with it, let us know where you are located.
Take heart... am sure you will find your place. 
(why is there a
icon LOL!!!)