When sewer is available at the street and your system needs major work, connection usually wins on total cost. Expect $5,000 to $15,000 including tap fees, plus a monthly sewer bill you did not have before.
More detail
The comparison is rarely as simple as connection cost against repair cost, because the two carry different ongoing obligations. Connection cost in Greater Columbus and Central Ohio generally breaks into three parts. The tap or capacity fee charged by the utility, which is often the largest single line and varies widely by district. The lateral run from the house to the main, priced by distance, depth, and what has to be crossed, since a driveway or mature landscaping adds meaningfully. And decommissioning the existing tank, which usually means pumping it and either crushing and filling it or removing it, per county requirement. Against that, a leach field replacement runs $5,000 to $12,000 and a full system replacement $8,000 to $15,000, with no monthly bill afterward and a service life measured in decades. The ongoing side is where it flips. Sewer service carries a monthly charge for as long as you own the house. Septic carries a pumping cost every three to five years and no monthly bill. Over twenty years the running costs are closer than most owners expect. The factor that overrides the arithmetic is whether connection is mandatory. Many jurisdictions require connection within a set period once sewer becomes available at the property line, or when an existing system fails, and some prohibit permitting a replacement system where sewer is accessible. That is a question for Septic permits, as-built drawings, and any point-of-sale requirement are held by the county health district covering the property, and they differ between districts across Franklin, Delaware, Licking, and Fairfield counties. One timing note: if your system is functioning and connection is not yet mandatory, there is no urgency. If it has failed and sewer is at the street, ask whether a replacement permit would even be issued before pricing the repair.