A new theater is coming to downtown Norristown next fall. The professional stage company Theatre Horizon plans to open a 120-seat house of its own, a $900,000 project being funded by private donors and audience members, plus Norristown and Montgomery County.

The company's cofounders and artistic directors, Erin Reilly and Matthew Decker, will officially announce the new theater, to be housed in the former Bell Telephone building next to the county courthouse at DeKalb and Penn Streets, at the opening Friday of Voices of Christmas. The show is running at the Centre Theater, a general-arts facility in Norristown.

Horizon has rented the top floor of that building for about half its seven-year existence; the company has staged shows in seven venues since its first production, The Laramie Project, in the auditorium of Upper Merion High School. Theatre Horizon is one of the region's fast-growing professional suburban companies, and this year it won four Barrymore Awards for its 25th Annual Putnam County Spelling Bee.

Horizon has never had its own theater. "The new theater will allow us new possibilities," Reilly said.

To help pay for the theater, Horizon was awarded a $200,000 grant from Norristown and Montgomery County revitalization funds. The company believes dining, parking, and other costs to audience members and the theater will return more than $65,000 a year to the borough.

The 1920s-vintage Bell building had been a line-switching station until about 15 years ago, then sat empty. Four years ago, two developers, Bob Kaufman and Mount Airy restaurateur Ken Weinstein, bought it, decided it would be appropriate in the arts district Norristown was trying to create along four blocks of DeKalb Street, and looked for an interested arts group. "Theater Horizon responded with enthusiasm," Kaufman said Thursday.