BROOMFIELD — Boulder County’s economy hummed with the confident energy of a finely tuned sports car in 1998.

Telecommunications and natural-foods companies gobbled up millions of dollars in venture capital. Upscale hotels popped up like sunflowers along the U.S. Highway 36 Corridor. Commercial and residential construction remained strong.

The event most people believed would have the most impact on the Boulder County economy didn’t surface until the end of the year. In November, Broomfield voters decided the city should secede from Boulder, Jefferson, Adams and Weld counties and become a city and a county of its own.

The move meant Boulder County lost a major source of sales tax revenue in FlatIron Crossing, the $200 million, upscale shopping center in Broomfield that opened in 2000.

Even so, county budgets rely more on property tax than on sales tax — and the impact could be somewhat mitigated because Boulder County would no longer have to provide services to Broomfield.

Still, concerns lingered:

• With the loss of the Interlocken business park, would Boulder County would lose some of its attractiveness as the Silicon Valley of the Rockies? Interlocken had just been selected for a huge Sun Microsystems Inc. campus and the headquarters of Level 3 Communication Inc., and the business park already was home to McData Corp. and other software and telecommunications firms.

• Because Broomfield County was planning to charge its businesses slightly lower property taxes than did Boulder County, would businesses move from the higher-cost county to the lower-cost one? That concern disappeared because Broomfield decided to match its property tax mill levy to Boulder County’s — the lowest of the four counties to which the city now belongs.

Broomfield decided to separate largely because it was tired of being an afterthought to each of the four counties as it grew. It felt especially spurned by Boulder County.

Becoming a city and county wasn’t cheap, however. It required Broomfield to build a new $6.6 million library, a new $11.8 million police and courts building, and a new $13.9 million jail.