Whether you’re talking colleagues or old camp friends, a wedding is such a personal affair that you should only invite the people you really want to come. So, sure, ask your office mates, but try to keep the chatter about the big day out of the office, and let your invited coworkers know not to mention it around others. If it does come up, focus on the process of wedding planning and not on the specific details of your own (“Who knew venues were so much cheaper on Fridays?”), or on items of general interest (“That new hotel downtown has an amazing bar—have you been?”). And use the phrase “It’s a small wedding” liberally.
The one sticky issue is your boss. If you collaborate closely with him or her, consider sending an invitation for political reasons. That said, never feel obligated to include anyone. It’s your day! Celebrate it with those you care about most.