More than 150 booths  highlighting area businesses, civic and service organizations, schools, churches, crafts, and other groups will line Meeting House Pond in Medfield Center  and North Street from Main Street to the Post Office from 8 a.m. to 4:30 p.m. on Sept. 15  as part of Discover Medfield Day festivities. Children’s activities will be in Kids’ Alley, open until 4 p.m. in the Montrose School  parking lot on North Street. The celebration also features a food court  and live entertainment. Registration remains open for booths, with 50 available on a first-come, first-served basis. The event is organized by Medfield Employers and Merchants Organization. Registration is available online at www.medfieldmemo.org; checks to secure a booth site must be paid within 10 days to MEMO, PO Box 6, Medfield, MA 02052,  or at Rockland Trust Bank branch on North Street. Walk-in registration is also accepted at the bank branch. The best-decorated booth can win a free exhibit site at next year’s Discover Medfield Day.