It's not too late to enroll your child in preschool. While our daughter had attended daycare first (when she was 2-3), she didn't start preschool until she was age 4. The preschool experience was so valuable for her social and academic development, and she had fun too (and as parents, we learned a lot as well)!
To learn more about your options for preschool, and to help prepare your family for this new stage of your daughter's development, here are some resources on Education.com I recommend you review:
To locate a preschool in our area when our daughter was that age, we asked our friends whose children were in preschool or whose children had previously attended preschool in our area. We also used Google and Yahoo to search for local preschools' contact information, and we participated in online parent communities (for first-hand testimonials of the schools we were considering), such as this one by the Berkeley Parents Network: http://parents.berkeley.edu/
If your family cannot afford preschool and you need low-income or free options, contact Head Start. Here is the Head Start locator on the U.S. Department of Health and Human Services website, to find a center near you: http://eclkc.ohs.acf.hhs.gov/hslc/HeadStartOffices .
You can try asking someone in your neighborhood to see if they know any good day cares. Or you can Google day cares, and set up appointments with the ones you like most (Read the reviews on their websites). Make sure you're happy with the daycare you choose!