Even if it's just a one-page site
It's critical to have an online presence. If you think about your own behaviour when deciding to use a business for their service - don't you check their website? Or at least their social pages? Having an online presence (a website, social media page, business listings, google maps) helps your business's credibility - it verifies that you are a trusted entity… (unless of course, your website looks like it was made in 1992, that's where I can help!).
At the very least have your company's logo, your contact details (vital!), and your business hours. Think about why people are looking for you in the first place - what do they need to know? What services or products do you provide? What do you want them to do? Would you prefer them to phone you or email you to contact you? Maybe you'd prefer them to fill out a form with pre-listed options?
Use your website as tool to educate your clients and customers as to what you do and how you'd like them to contact you.